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2013-10-15rcu: Move RCU-related source code to kernel/rcu directoryPaul E. McKenney
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Ingo Molnar <mingo@kernel.org>
2013-10-15Merge branch 'idle.2013.09.25a' into HEADPaul E. McKenney
idle.2013.09.25a: Topic branch for idle entry-/exit-related changes.
2013-10-15Merge branch 'gp.2013.09.25a' into HEADPaul E. McKenney
gp.2013.09.25a: Topic branch for grace-period updates.
2013-09-25rcu: Consistent rcu_is_watching() namingPaul E. McKenney
The old rcu_is_cpu_idle() function is just __rcu_is_watching() with preemption disabled. This commit therefore renames rcu_is_cpu_idle() to rcu_is_watching. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-09-25rcu: Change EXPORT_SYMBOL() to EXPORT_SYMBOL_GPL()Paul E. McKenney
Commit e6b80a3b (rcu: Detect illegal rcu dereference in extended quiescent state) exported the pre-existing rcu_is_cpu_idle() function using EXPORT_SYMBOL(). However, this is inconsistent with the remaining exports from RCU, which are all EXPORT_SYMBOL_GPL(). The current state of affairs means that a non-GPL module could use rcu_is_cpu_idle(), but in a CONFIG_TREE_PREEMPT_RCU=y kernel would be unable to invoke rcu_read_lock() and rcu_read_unlock(). This commit therefore makes rcu_is_cpu_idle()'s export be consistent with the rest of RCU, namely EXPORT_SYMBOL_GPL(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-09-25rcu: Is it safe to enter an RCU read-side critical section?Paul E. McKenney
There is currently no way for kernel code to determine whether it is safe to enter an RCU read-side critical section, in other words, whether or not RCU is paying attention to the currently running CPU. Given the large and increasing quantity of code shared by the idle loop and non-idle code, the this shortcoming is becoming increasingly painful. This commit therefore adds __rcu_is_watching(), which returns true if it is safe to enter an RCU read-side critical section on the currently running CPU. This function is quite fast, using only a __this_cpu_read(). However, the caller must disable preemption. Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-09-23rcu: Add tracing of normal (non-NOCB) grace-period requestsPaul E. McKenney
This commit adds tracing to the normal grace-period request points. These are rcu_gp_cleanup(), which checks for the need for another grace period at the end of the previous grace period, and rcu_start_gp_advanced(), which restarts RCU's state machine after an idle period. These trace events are intended to help track down bugs where RCU remains idle despite there being work for it to do. Reported-by: Clark Williams <williams@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-09-23rcu: Add tracing to rcu_gp_kthread()Paul E. McKenney
This commit adds tracing to the rcu_gp_kthread() function in order to help trace down hangs potentially involving this kthread. Reported-by: Clark Williams <williams@redhat.com> Reported-by: Carsten Emde <C.Emde@osadl.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-09-23rcu: Flag lockless access to ->gp_flags with ACCESS_ONCE()Paul E. McKenney
This commit applies ACCESS_ONCE() to an outside-of-lock access to ->gp_flags. Although it is hard to imagine any sane compiler messing this particular case up, the documentation benefits are substantial. Plus the definition of "sane compiler" grows ever looser. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-09-23rcu: Prevent spurious-wakeup DoS attack on rcu_gp_kthread()Paul E. McKenney
Spurious wakeups in the force-quiescent-state loop in rcu_gp_kthread() cause the timeout to be recalculated, which would prevent rcu_gp_fqs() from ever being called. This would in turn would prevent the grace period from ever ending for as long as there was at least one CPU in an extended quiescent state that had not yet passed through a quiescent state. This commit therefore avoids recalculating the timeout unless the previous pass's call to wait_event_interruptible_timeout() actually did time out, thus preventing the above scenario. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-09-23rcu: Improve grace-period start logicPaul E. McKenney
This commit improves grace-period start logic by checking ->gp_flags under the lock and by issuing a warning if a grace period is already in progress. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-09-23rcu: Have rcutiny tracepoints use tracepoint_string()Paul E. McKenney
This commit extends the work done in f7f7bac9 (rcu: Have the RCU tracepoints use the tracepoint_string infrastructure) to cover rcutiny. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org>
2013-09-23rcu: Reject memory-order-induced stall-warning false positivesPaul E. McKenney
If a system is idle from an RCU perspective for longer than specified by CONFIG_RCU_CPU_STALL_TIMEOUT, and if one CPU starts a grace period just as a second checks for CPU stalls, and if this second CPU happens to see the old value of rsp->jiffies_stall, it will incorrectly report a CPU stall. This is quite rare, but apparently occurs deterministically on systems with about 6TB of memory. This commit therefore orders accesses to the data used to determine whether or not a CPU stall is in progress. Grace-period initialization and cleanup first increments rsp->completed to mark the end of the previous grace period, then records the current jiffies in rsp->gp_start, then records the jiffies at which a stall can be expected to occur in rsp->jiffies_stall, and finally increments rsp->gpnum to mark the start of the new grace period. Now, this ordering by itself does not prevent false positives. For example, if grace-period initialization was delayed between recording rsp->gp_start and rsp->jiffies_stall, the CPU stall warning code might still see an old value of rsp->jiffies_stall. Therefore, this commit also orders the CPU stall warning accesses as well, loading rsp->gpnum and jiffies, then rsp->jiffies_stall, then rsp->gp_start, and finally rsp->completed. This ordering means that the false-positive scenario in the previous paragraph would result in rsp->completed being greater than or equal to rsp->gpnum, which is never valid for a CPU stall, allowing the false positive to be rejected. Furthermore, any fetch that gets an old value of rsp->jiffies_stall must also get an old value of rsp->gpnum, which will again be rejected by the comparison of rsp->gpnum and rsp->completed. Situations where rsp->gp_start is later than rsp->jiffies_stall are also rejected, as are situations where jiffies is less than rsp->jiffies_stall. Although use of unsynchronized accesses means that there are likely still some false-positive scenarios (synchronization has proven to be a very bad idea on large systems), this should get rid of a large class of these scenarios. Reported-by: Fabian Herschel <fabian.herschel@suse.com> Reported-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Michal Hocko <mhocko@suse.cz> Tested-by: Jochen Striepe <jochen@tolot.escape.de>
2013-09-23rcu: Micro-optimize rcu_cpu_has_callbacks()Paul E. McKenney
The for_each_rcu_flavor() loop unconditionally scans all flavors, even when the first flavor might have some non-lazy callbacks. Once the loop has seen a non-lazy callback, further passes through the loop cannot change the state. This is not a huge problem, given that there can be at most three RCU flavors (RCU-bh, RCU-preempt, and RCU-sched), but this code is on the path to idle, so speeding it up even a small amount would have some benefit. This commit therefore does two things: 1. Rearranges the order of the list of RCU flavors in order to place the most active flavor first in the list. The most active RCU flavor is RCU-preempt, or, if there is no RCU-preempt, RCU-sched. 2. Reworks the for_each_rcu_flavor() to exit early when the first non-lazy callback is seen, or, in the case where the caller does not care about non-lazy callbacks (RCU_FAST_NO_HZ=n), when the first callback is seen. Reported-by: Chen Gang <gang.chen@asianux.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-09-23rcu: Silence unused-variable warningsPaul E. McKenney
The "idle" variable in both rcu_eqs_enter_common() and rcu_eqs_exit_common() is only used in a WARN_ON_ONCE(). If the kernel is built disabling WARN_ON_ONCE(), the compiler will complain (rightly) that "idle" is unused. This commit therefore adds a __maybe_unused to the declaration of both variables. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-09-23rcu: Replace __get_cpu_var() usesChristoph Lameter
__get_cpu_var() is used for multiple purposes in the kernel source. One of them is address calculation via the form &__get_cpu_var(x). This calculates the address for the instance of the percpu variable of the current processor based on an offset. Other use cases are for storing and retrieving data from the current processors percpu area. __get_cpu_var() can be used as an lvalue when writing data or on the right side of an assignment. __get_cpu_var() is defined as : __get_cpu_var() always only does an address determination. However, store and retrieve operations could use a segment prefix (or global register on other platforms) to avoid the address calculation. this_cpu_write() and this_cpu_read() can directly take an offset into a percpu area and use optimized assembly code to read and write per cpu variables. This patch converts __get_cpu_var into either an explicit address calculation using this_cpu_ptr() or into a use of this_cpu operations that use the offset. Thereby address calcualtions are avoided and less registers are used when code is generated. At the end of the patchset all uses of __get_cpu_var have been removed so the macro is removed too. The patchset includes passes over all arches as well. Once these operations are used throughout then specialized macros can be defined in non -x86 arches as well in order to optimize per cpu access by f.e. using a global register that may be set to the per cpu base. Transformations done to __get_cpu_var() 1. Determine the address of the percpu instance of the current processor. DEFINE_PER_CPU(int, y); int *x = &__get_cpu_var(y); Converts to int *x = this_cpu_ptr(&y); 2. Same as #1 but this time an array structure is involved. DEFINE_PER_CPU(int, y[20]); int *x = __get_cpu_var(y); Converts to int *x = this_cpu_ptr(y); 3. Retrieve the content of the current processors instance of a per cpu variable. DEFINE_PER_CPU(int, u); int x = __get_cpu_var(y) Converts to int x = __this_cpu_read(y); 4. Retrieve the content of a percpu struct DEFINE_PER_CPU(struct mystruct, y); struct mystruct x = __get_cpu_var(y); Converts to memcpy(this_cpu_ptr(&x), y, sizeof(x)); 5. Assignment to a per cpu variable DEFINE_PER_CPU(int, y) __get_cpu_var(y) = x; Converts to this_cpu_write(y, x); 6. Increment/Decrement etc of a per cpu variable DEFINE_PER_CPU(int, y); __get_cpu_var(y)++ Converts to this_cpu_inc(y) Signed-off-by: Christoph Lameter <cl@linux.com> [ paulmck: Address conflicts. ] Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-09-23rcu: Convert local functions to staticPaul E. McKenney
The rcu_cpu_stall_timeout kernel parameter, the rcu_dynticks per-CPU variable, and the rcu_gp_fqs() function are used only locally. This commit therefore marks them as static. Reported-by: kbuild test robot <fengguang.wu@intel.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-09-20rcu: Use proper cpp macro for ->gp_flagsPaul E. McKenney
One of the ->gp_flags assignments used a raw number rather than the cpp macro that was intended for this purpose, which this commit fixes. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-08-31Merge branches 'doc.2013.08.19a', 'fixes.2013.08.20a', 'sysidle.2013.08.31a' ↵Paul E. McKenney
and 'torture.2013.08.20a' into HEAD doc.2013.08.19a: Documentation updates fixes.2013.08.20a: Miscellaneous fixes sysidle.2013.08.31a: Detect system-wide idle state. torture.2013.08.20a: rcutorture updates.
2013-08-31nohz_full: Force RCU's grace-period kthreads onto timekeeping CPUPaul E. McKenney
Because RCU's quiescent-state-forcing mechanism is used to drive the full-system-idle state machine, and because this mechanism is executed by RCU's grace-period kthreads, this commit forces these kthreads to run on the timekeeping CPU (tick_do_timer_cpu). To do otherwise would mean that the RCU grace-period kthreads would force the system into non-idle state every time they drove the state machine, which would be just a bit on the futile side. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-31nohz_full: Add full-system-idle state machinePaul E. McKenney
This commit adds the state machine that takes the per-CPU idle data as input and produces a full-system-idle indication as output. This state machine is driven out of RCU's quiescent-state-forcing mechanism, which invokes rcu_sysidle_check_cpu() to collect per-CPU idle state and then rcu_sysidle_report() to drive the state machine. The full-system-idle state is sampled using rcu_sys_is_idle(), which also drives the state machine if RCU is idle (and does so by forcing RCU to become non-idle). This function returns true if all but the timekeeping CPU (tick_do_timer_cpu) are idle and have been idle long enough to avoid memory contention on the full_sysidle_state state variable. The rcu_sysidle_force_exit() may be called externally to reset the state machine back into non-idle state. For large systems the state machine is driven out of RCU's force-quiescent-state logic, which provides good scalability at the price of millisecond-scale latencies on the transition to full-system-idle state. This is not so good for battery-powered systems, which are usually small enough that they don't need to care about scalability, but which do care deeply about energy efficiency. Small systems therefore drive the state machine directly out of the idle-entry code. The number of CPUs in a "small" system is defined by a new NO_HZ_FULL_SYSIDLE_SMALL Kconfig parameter, which defaults to 8. Note that this is a build-time definition. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> [ paulmck: Use true and false for boolean constants per Lai Jiangshan. ] Reviewed-by: Josh Triplett <josh@joshtriplett.org> [ paulmck: Simplify logic and provide better comments for memory barriers, based on review comments and questions by Lai Jiangshan. ]
2013-08-20rcu: Simplify _rcu_barrier() processingPaul E. McKenney
This commit drops an unneeded ACCESS_ONCE() and simplifies an "our work is done" check in _rcu_barrier(). This applies feedback from Linus (https://lkml.org/lkml/2013/7/26/777) that he gave to similar code in an unrelated patch. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> [ paulmck: Fix comment to match code, reported by Lai Jiangshan. ]
2013-08-18nohz_full: Add full-system-idle arguments to APIPaul E. McKenney
This commit adds an isidle and jiffies argument to force_qs_rnp(), dyntick_save_progress_counter(), and rcu_implicit_dynticks_qs() to enable RCU's force-quiescent-state process to check for full-system idle. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> [ paulmck: Use true and false for boolean constants per Lai Jiangshan. ] Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-18nohz_full: Add per-CPU idle-state trackingPaul E. McKenney
This commit adds the code that updates the rcu_dyntick structure's new fields to track the per-CPU idle state based on interrupts and transitions into and out of the idle loop (NMIs are ignored because NMI handlers cannot cleanly read out the time anyway). This code is similar to the code that maintains RCU's idea of per-CPU idleness, but differs in that RCU treats CPUs running in user mode as idle, where this new code does not. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-18nohz_full: Add rcu_dyntick data for scalable detection of all-idle statePaul E. McKenney
This commit adds fields to the rcu_dyntick structure that are used to detect idle CPUs. These new fields differ from the existing ones in that the existing ones consider a CPU executing in user mode to be idle, where the new ones consider CPUs executing in user mode to be busy. The handling of these new fields is otherwise quite similar to that for the exiting fields. This commit also adds the initialization required for these fields. So, why is usermode execution treated differently, with RCU considering it a quiescent state equivalent to idle, while in contrast the new full-system idle state detection considers usermode execution to be non-idle? It turns out that although one of RCU's quiescent states is usermode execution, it is not a full-system idle state. This is because the purpose of the full-system idle state is not RCU, but rather determining when accurate timekeeping can safely be disabled. Whenever accurate timekeeping is required in a CONFIG_NO_HZ_FULL kernel, at least one CPU must keep the scheduling-clock tick going. If even one CPU is executing in user mode, accurate timekeeping is requires, particularly for architectures where gettimeofday() and friends do not enter the kernel. Only when all CPUs are really and truly idle can accurate timekeeping be disabled, allowing all CPUs to turn off the scheduling clock interrupt, thus greatly improving energy efficiency. This naturally raises the question "Why is this code in RCU rather than in timekeeping?", and the answer is that RCU has the data and infrastructure to efficiently make this determination. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-18rcu: Eliminate unused APIs intended for adaptive ticksPaul E. McKenney
The rcu_user_enter_after_irq() and rcu_user_exit_after_irq() functions were intended for use by adaptive ticks, but changes in implementation have rendered them unnecessary. This commit therefore removes them. Reported-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-18rcu: Avoid redundant grace-period kthread wakeupsPaul E. McKenney
When setting up an in-the-future "advanced" grace period, the code needs to wake up the relevant grace-period kthread, which it currently does unconditionally. However, this results in needless wakeups in the case where the advanced grace period is being set up by the grace-period kthread itself, which is a non-uncommon situation. This commit therefore checks to see if the running thread is the grace-period kthread, and avoids doing the irq_work_queue()-mediated wakeup in that case. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-18rcu: Make call_rcu() leak callbacks for debug-object errorsPaul E. McKenney
If someone does a duplicate call_rcu(), the worst thing the second call_rcu() could do would be to actually queue the callback the second time because doing so corrupts whatever list the callback was already queued on. This commit therefore makes __call_rcu() check the new return value from debug-objects and leak the callback upon error. This commit also substitutes rcu_leak_callback() for whatever callback function was previously in place in order to avoid freeing the callback out from under any readers that might still be referencing it. These changes increase the probability that the debug-objects error messages will actually make it somewhere visible. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Sedat Dilek <sedat.dilek@gmail.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Rik van Riel <riel@surriel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-08-18rcu: Expedite grace periods during suspend/resumeBorislav Petkov
CONFIG_RCU_FAST_NO_HZ can increase grace-period durations by up to a factor of four, which can result in long suspend and resume times. Thus, this commit temporarily switches to expedited grace periods when suspending the box and return to normal settings when resuming. Similar logic is applied to hibernation. Because expedited grace periods are of dubious benefit on very large systems, so this commit restricts their automated use during suspend and resume to systems of 256 or fewer CPUs. (Some day a number of Linux-kernel facilities, including RCU's expedited grace periods, will be more scalable, but I need to see bug reports first.) [ paulmck: This also papers over an audio/irq bug, but hopefully that will be fixed soon. ] Signed-off-by: Borislav Petkov <bp@suse.de> Signed-off-by: Bjørn Mork <bjorn@mork.no> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-07-29rcu: Have the RCU tracepoints use the tracepoint_string infrastructureSteven Rostedt (Red Hat)
Currently, RCU tracepoints save only a pointer to strings in the ring buffer. When displayed via the /sys/kernel/debug/tracing/trace file they are referenced like the printf "%s" that looks at the address in the ring buffer and prints out the string it points too. This requires that the strings are constant and persistent in the kernel. The problem with this is for tools like trace-cmd and perf that read the binary data from the buffers but have no access to the kernel memory to find out what string is represented by the address in the buffer. By using the tracepoint_string infrastructure, the RCU tracepoint strings can be exported such that userspace tools can map the addresses to the strings. # cat /sys/kernel/debug/tracing/printk_formats 0xffffffff81a4a0e8 : "rcu_preempt" 0xffffffff81a4a0f4 : "rcu_bh" 0xffffffff81a4a100 : "rcu_sched" 0xffffffff818437a0 : "cpuqs" 0xffffffff818437a6 : "rcu_sched" 0xffffffff818437a0 : "cpuqs" 0xffffffff818437b0 : "rcu_bh" 0xffffffff818437b7 : "Start context switch" 0xffffffff818437cc : "End context switch" 0xffffffff818437a0 : "cpuqs" [...] Now userspaces tools can display: rcu_utilization: Start context switch rcu_dyntick: Start 1 0 rcu_utilization: End context switch rcu_batch_start: rcu_preempt CBs=0/5 bl=10 rcu_dyntick: End 0 140000000000000 rcu_invoke_callback: rcu_preempt rhp=0xffff880071c0d600 func=proc_i_callback rcu_invoke_callback: rcu_preempt rhp=0xffff880077b5b230 func=__d_free rcu_dyntick: Start 140000000000000 0 rcu_invoke_callback: rcu_preempt rhp=0xffff880077563980 func=file_free_rcu rcu_batch_end: rcu_preempt CBs-invoked=3 idle=>c<>c<>c<>c< rcu_utilization: End RCU core rcu_grace_period: rcu_preempt 9741 start rcu_dyntick: Start 1 0 rcu_dyntick: End 0 140000000000000 rcu_dyntick: Start 140000000000000 0 Instead of: rcu_utilization: ffffffff81843110 rcu_future_grace_period: ffffffff81842f1d 9939 9939 9940 0 0 3 ffffffff81842f32 rcu_batch_start: ffffffff81842f1d CBs=0/4 bl=10 rcu_future_grace_period: ffffffff81842f1d 9939 9939 9940 0 0 3 ffffffff81842f3c rcu_grace_period: ffffffff81842f1d 9939 ffffffff81842f80 rcu_invoke_callback: ffffffff81842f1d rhp=0xffff88007888aac0 func=file_free_rcu rcu_grace_period: ffffffff81842f1d 9939 ffffffff81842f95 rcu_invoke_callback: ffffffff81842f1d rhp=0xffff88006aeb4600 func=proc_i_callback rcu_future_grace_period: ffffffff81842f1d 9939 9939 9940 0 0 3 ffffffff81842f32 rcu_future_grace_period: ffffffff81842f1d 9939 9939 9940 0 0 3 ffffffff81842f3c rcu_invoke_callback: ffffffff81842f1d rhp=0xffff880071cb9fc0 func=__d_free rcu_grace_period: ffffffff81842f1d 9939 ffffffff81842f80 rcu_invoke_callback: ffffffff81842f1d rhp=0xffff88007888ae80 func=file_free_rcu rcu_batch_end: ffffffff81842f1d CBs-invoked=4 idle=>c<>c<>c<>c< rcu_utilization: ffffffff8184311f Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-07-29rcu: Simplify RCU_STATE_INITIALIZER() macroSteven Rostedt (Red Hat)
The RCU_STATE_INITIALIZER() macro is used only in the rcutree.c file as well as the rcutree_plugin.h file. It is passed as a rvalue to a variable of a similar name. A per_cpu variable is also created with a similar name as well. The uses of RCU_STATE_INITIALIZER() can be simplified to remove some of the duplicate code that is done. Currently the three users of this macro has this format: struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched, call_rcu_sched); DEFINE_PER_CPU(struct rcu_data, rcu_sched_data); Notice that "rcu_sched" is called three times. This is the same with the other two users. This can be condensed to just: RCU_STATE_INITIALIZER(rcu_sched, call_rcu_sched); by moving the rest into the macro itself. This also opens the door to allow the RCU tracepoint strings and their addresses to be exported so that userspace tracing tools can translate the contents of the pointers of the RCU tracepoints. The change will allow for helper code to be placed in the RCU_STATE_INITIALIZER() macro to export the name that is used. Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-07-29rcu: Add const annotation to char * for RCU tracepoints and functionsSteven Rostedt (Red Hat)
All the RCU tracepoints and functions that reference char pointers do so with just 'char *' even though they do not modify the contents of the string itself. This will cause warnings if a const char * is used in one of these functions. The RCU tracepoints store the pointer to the string to refer back to them when the trace output is displayed. As this can be minutes, hours or even days later, those strings had better be constant. This change also opens the door to allow the RCU tracepoint strings and their addresses to be exported so that userspace tracing tools can translate the contents of the pointers of the RCU tracepoints. Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-07-14rcu: delete __cpuinit usage from all rcu filesPaul Gortmaker
The __cpuinit type of throwaway sections might have made sense some time ago when RAM was more constrained, but now the savings do not offset the cost and complications. For example, the fix in commit 5e427ec2d0 ("x86: Fix bit corruption at CPU resume time") is a good example of the nasty type of bugs that can be created with improper use of the various __init prefixes. After a discussion on LKML[1] it was decided that cpuinit should go the way of devinit and be phased out. Once all the users are gone, we can then finally remove the macros themselves from linux/init.h. This removes all the drivers/rcu uses of the __cpuinit macros from all C files. [1] https://lkml.org/lkml/2013/5/20/589 Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Josh Triplett <josh@freedesktop.org> Cc: Dipankar Sarma <dipankar@in.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
2013-07-03drivers: avoid parsing names as kthread_run() format stringsKees Cook
Calling kthread_run with a single name parameter causes it to be handled as a format string. Many callers are passing potentially dynamic string content, so use "%s" in those cases to avoid any potential accidents. Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-06-10Merge branches 'cbnum.2013.06.10a', 'doc.2013.06.10a', 'fixes.2013.06.10a', ↵Paul E. McKenney
'srcu.2013.06.10a' and 'tiny.2013.06.10a' into HEAD cbnum.2013.06.10a: Apply simplifications stemming from the new callback numbering. doc.2013.06.10a: Documentation updates. fixes.2013.06.10a: Miscellaneous fixes. srcu.2013.06.10a: Updates to SRCU. tiny.2013.06.10a: Eliminate TINY_PREEMPT_RCU.
2013-06-10rcu: Drive quiescent-state-forcing delay from HZPaul E. McKenney
Systems with HZ=100 can have slow bootup times due to the default three-jiffy delays between quiescent-state forcing attempts. This commit therefore auto-tunes the RCU_JIFFIES_TILL_FORCE_QS value based on the value of HZ. However, this would break very large systems that require more time between quiescent-state forcing attempts. This commit therefore also ups the default delay by one jiffy for each 256 CPUs that might be on the system (based off of nr_cpu_ids at runtime, -not- NR_CPUS at build time). Updated to collapse #ifdefs for RCU_JIFFIES_TILL_FORCE_QS into a step-function definition as suggested by Josh Triplett. Reported-by: Paul Mackerras <paulus@au1.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-06-10rcu: Move redundant call to note_gp_changes() into called functionPaul E. McKenney
The __rcu_process_callbacks() invokes note_gp_changes() immediately before invoking rcu_check_quiescent_state(), which conditionally invokes that same function. This commit therefore eliminates the call to note_gp_changes() in __rcu_process_callbacks() in favor of making unconditional to call from rcu_check_quiescent_state() to note_gp_changes(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Inline trivial wrapper function rcu_start_gp_per_cpu()Paul E. McKenney
Given the changes that introduce note_gp_change(), rcu_start_gp_per_cpu() is now a trivial wrapper function with only one caller. This commit therefore inlines it into its sole call site. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Eliminate check_for_new_grace_period() wrapper functionPaul E. McKenney
One of the calls to check_for_new_grace_period() is now redundant due to an immediately preceding call to note_gp_changes(). Eliminating this redundant call leaves a single caller, which is simpler if inlined. This commit therefore eliminates the redundant call and inlines the body of check_for_new_grace_period() into the single remaining call site. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Merge __rcu_process_gp_end() into __note_gp_changes()Paul E. McKenney
This commit eliminates some duplicated code by merging __rcu_process_gp_end() into __note_gp_changes(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Switch callers from rcu_process_gp_end() to note_gp_changes()Paul E. McKenney
Because note_gp_changes() now incorporates rcu_process_gp_end() function, this commit switches to the former and eliminates the latter. In addition, this commit changes external calls from __rcu_process_gp_end() to __note_gp_changes(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Rename note_new_gpnum() to note_gp_changes()Paul E. McKenney
Because note_new_gpnum() now also checks for the ends of old grace periods, this commit changes its name to note_gp_changes(). Later commits will merge rcu_process_gp_end() into note_gp_changes(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Make __note_new_gpnum() check for ends of prior grace periodsPaul E. McKenney
The current implementation can detect the beginning of a new grace period before noting the end of a previous grace period. Although the current implementation correctly handles this sort of nonsense, it would be good to reduce RCU's state space by making such nonsense unnecessary, which is now possible thanks to the fact that RCU's callback groups are now numbered. This commit therefore makes __note_new_gpnum() invoke __rcu_process_gp_end() in order to note the ends of prior grace periods before noting the beginnings of new grace periods. Of course, this now means that note_new_gpnum() notes both the beginnings and ends of grace periods, and could therefore be used in place of rcu_process_gp_end(). But that is a job for later commits. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Move code to apply callback-numbering simplificationsPaul E. McKenney
The addition of callback numbering allows combining the detection of the ends of old grace periods and the beginnings of new grace periods. This commit moves code to set the stage for this combining. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Convert rcutree.c printk callsPaul E. McKenney
This commit converts printk() calls to the corresponding pr_*() calls. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10rcu: Fix deadlock with CPU hotplug, RCU GP init, and timer migrationPaul E. McKenney
In Steven Rostedt's words: > I've been debugging the last couple of days why my tests have been > locking up. One of my tracing tests, runs all available tracers. The > lockup always happened with the mmiotrace, which is used to trace > interactions between priority drivers and the kernel. But to do this > easily, when the tracer gets registered, it disables all but the boot > CPUs. The lockup always happened after it got done disabling the CPUs. > > Then I decided to try this: > > while :; do > for i in 1 2 3; do > echo 0 > /sys/devices/system/cpu/cpu$i/online > done > for i in 1 2 3; do > echo 1 > /sys/devices/system/cpu/cpu$i/online > done > done > > Well, sure enough, that locked up too, with the same users. Doing a > sysrq-w (showing all blocked tasks): > > [ 2991.344562] task PC stack pid father > [ 2991.344562] rcu_preempt D ffff88007986fdf8 0 10 2 0x00000000 > [ 2991.344562] ffff88007986fc98 0000000000000002 ffff88007986fc48 0000000000000908 > [ 2991.344562] ffff88007986c280 ffff88007986ffd8 ffff88007986ffd8 00000000001d3c80 > [ 2991.344562] ffff880079248a40 ffff88007986c280 0000000000000000 00000000fffd4295 > [ 2991.344562] Call Trace: > [ 2991.344562] [<ffffffff815437ba>] schedule+0x64/0x66 > [ 2991.344562] [<ffffffff81541750>] schedule_timeout+0xbc/0xf9 > [ 2991.344562] [<ffffffff8154bec0>] ? ftrace_call+0x5/0x2f > [ 2991.344562] [<ffffffff81049513>] ? cascade+0xa8/0xa8 > [ 2991.344562] [<ffffffff815417ab>] schedule_timeout_uninterruptible+0x1e/0x20 > [ 2991.344562] [<ffffffff810c980c>] rcu_gp_kthread+0x502/0x94b > [ 2991.344562] [<ffffffff81062791>] ? __init_waitqueue_head+0x50/0x50 > [ 2991.344562] [<ffffffff810c930a>] ? rcu_gp_fqs+0x64/0x64 > [ 2991.344562] [<ffffffff81061cdb>] kthread+0xb1/0xb9 > [ 2991.344562] [<ffffffff81091e31>] ? lock_release_holdtime.part.23+0x4e/0x55 > [ 2991.344562] [<ffffffff81061c2a>] ? __init_kthread_worker+0x58/0x58 > [ 2991.344562] [<ffffffff8154c1dc>] ret_from_fork+0x7c/0xb0 > [ 2991.344562] [<ffffffff81061c2a>] ? __init_kthread_worker+0x58/0x58 > [ 2991.344562] kworker/0:1 D ffffffff81a30680 0 47 2 0x00000000 > [ 2991.344562] Workqueue: events cpuset_hotplug_workfn > [ 2991.344562] ffff880078dbbb58 0000000000000002 0000000000000006 00000000000000d8 > [ 2991.344562] ffff880078db8100 ffff880078dbbfd8 ffff880078dbbfd8 00000000001d3c80 > [ 2991.344562] ffff8800779ca5c0 ffff880078db8100 ffffffff81541fcf 0000000000000000 > [ 2991.344562] Call Trace: > [ 2991.344562] [<ffffffff81541fcf>] ? __mutex_lock_common+0x3d4/0x609 > [ 2991.344562] [<ffffffff815437ba>] schedule+0x64/0x66 > [ 2991.344562] [<ffffffff81543a39>] schedule_preempt_disabled+0x18/0x24 > [ 2991.344562] [<ffffffff81541fcf>] __mutex_lock_common+0x3d4/0x609 > [ 2991.344562] [<ffffffff8103d11b>] ? get_online_cpus+0x3c/0x50 > [ 2991.344562] [<ffffffff8103d11b>] ? get_online_cpus+0x3c/0x50 > [ 2991.344562] [<ffffffff815422ff>] mutex_lock_nested+0x3b/0x40 > [ 2991.344562] [<ffffffff8103d11b>] get_online_cpus+0x3c/0x50 > [ 2991.344562] [<ffffffff810af7e6>] rebuild_sched_domains_locked+0x6e/0x3a8 > [ 2991.344562] [<ffffffff810b0ec6>] rebuild_sched_domains+0x1c/0x2a > [ 2991.344562] [<ffffffff810b109b>] cpuset_hotplug_workfn+0x1c7/0x1d3 > [ 2991.344562] [<ffffffff810b0ed9>] ? cpuset_hotplug_workfn+0x5/0x1d3 > [ 2991.344562] [<ffffffff81058e07>] process_one_work+0x2d4/0x4d1 > [ 2991.344562] [<ffffffff81058d3a>] ? process_one_work+0x207/0x4d1 > [ 2991.344562] [<ffffffff8105964c>] worker_thread+0x2e7/0x3b5 > [ 2991.344562] [<ffffffff81059365>] ? rescuer_thread+0x332/0x332 > [ 2991.344562] [<ffffffff81061cdb>] kthread+0xb1/0xb9 > [ 2991.344562] [<ffffffff81061c2a>] ? __init_kthread_worker+0x58/0x58 > [ 2991.344562] [<ffffffff8154c1dc>] ret_from_fork+0x7c/0xb0 > [ 2991.344562] [<ffffffff81061c2a>] ? __init_kthread_worker+0x58/0x58 > [ 2991.344562] bash D ffffffff81a4aa80 0 2618 2612 0x10000000 > [ 2991.344562] ffff8800379abb58 0000000000000002 0000000000000006 0000000000000c2c > [ 2991.344562] ffff880077fea140 ffff8800379abfd8 ffff8800379abfd8 00000000001d3c80 > [ 2991.344562] ffff8800779ca5c0 ffff880077fea140 ffffffff81541fcf 0000000000000000 > [ 2991.344562] Call Trace: > [ 2991.344562] [<ffffffff81541fcf>] ? __mutex_lock_common+0x3d4/0x609 > [ 2991.344562] [<ffffffff815437ba>] schedule+0x64/0x66 > [ 2991.344562] [<ffffffff81543a39>] schedule_preempt_disabled+0x18/0x24 > [ 2991.344562] [<ffffffff81541fcf>] __mutex_lock_common+0x3d4/0x609 > [ 2991.344562] [<ffffffff81530078>] ? rcu_cpu_notify+0x2f5/0x86e > [ 2991.344562] [<ffffffff81530078>] ? rcu_cpu_notify+0x2f5/0x86e > [ 2991.344562] [<ffffffff815422ff>] mutex_lock_nested+0x3b/0x40 > [ 2991.344562] [<ffffffff81530078>] rcu_cpu_notify+0x2f5/0x86e > [ 2991.344562] [<ffffffff81091c99>] ? __lock_is_held+0x32/0x53 > [ 2991.344562] [<ffffffff81548912>] notifier_call_chain+0x6b/0x98 > [ 2991.344562] [<ffffffff810671fd>] __raw_notifier_call_chain+0xe/0x10 > [ 2991.344562] [<ffffffff8103cf64>] __cpu_notify+0x20/0x32 > [ 2991.344562] [<ffffffff8103cf8d>] cpu_notify_nofail+0x17/0x36 > [ 2991.344562] [<ffffffff815225de>] _cpu_down+0x154/0x259 > [ 2991.344562] [<ffffffff81522710>] cpu_down+0x2d/0x3a > [ 2991.344562] [<ffffffff81526351>] store_online+0x4e/0xe7 > [ 2991.344562] [<ffffffff8134d764>] dev_attr_store+0x20/0x22 > [ 2991.344562] [<ffffffff811b3c5f>] sysfs_write_file+0x108/0x144 > [ 2991.344562] [<ffffffff8114c5ef>] vfs_write+0xfd/0x158 > [ 2991.344562] [<ffffffff8114c928>] SyS_write+0x5c/0x83 > [ 2991.344562] [<ffffffff8154c494>] tracesys+0xdd/0xe2 > > As well as held locks: > > [ 3034.728033] Showing all locks held in the system: > [ 3034.728033] 1 lock held by rcu_preempt/10: > [ 3034.728033] #0: (rcu_preempt_state.onoff_mutex){+.+...}, at: [<ffffffff810c9471>] rcu_gp_kthread+0x167/0x94b > [ 3034.728033] 4 locks held by kworker/0:1/47: > [ 3034.728033] #0: (events){.+.+.+}, at: [<ffffffff81058d3a>] process_one_work+0x207/0x4d1 > [ 3034.728033] #1: (cpuset_hotplug_work){+.+.+.}, at: [<ffffffff81058d3a>] process_one_work+0x207/0x4d1 > [ 3034.728033] #2: (cpuset_mutex){+.+.+.}, at: [<ffffffff810b0ec1>] rebuild_sched_domains+0x17/0x2a > [ 3034.728033] #3: (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8103d11b>] get_online_cpus+0x3c/0x50 > [ 3034.728033] 1 lock held by mingetty/2563: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > [ 3034.728033] 1 lock held by mingetty/2565: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > [ 3034.728033] 1 lock held by mingetty/2569: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > [ 3034.728033] 1 lock held by mingetty/2572: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > [ 3034.728033] 1 lock held by mingetty/2575: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > [ 3034.728033] 7 locks held by bash/2618: > [ 3034.728033] #0: (sb_writers#5){.+.+.+}, at: [<ffffffff8114bc3f>] file_start_write+0x2a/0x2c > [ 3034.728033] #1: (&buffer->mutex#2){+.+.+.}, at: [<ffffffff811b3b93>] sysfs_write_file+0x3c/0x144 > [ 3034.728033] #2: (s_active#54){.+.+.+}, at: [<ffffffff811b3c3e>] sysfs_write_file+0xe7/0x144 > [ 3034.728033] #3: (x86_cpu_hotplug_driver_mutex){+.+.+.}, at: [<ffffffff810217c2>] cpu_hotplug_driver_lock+0x17/0x19 > [ 3034.728033] #4: (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff8103d196>] cpu_maps_update_begin+0x17/0x19 > [ 3034.728033] #5: (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8103cfd8>] cpu_hotplug_begin+0x2c/0x6d > [ 3034.728033] #6: (rcu_preempt_state.onoff_mutex){+.+...}, at: [<ffffffff81530078>] rcu_cpu_notify+0x2f5/0x86e > [ 3034.728033] 1 lock held by bash/2980: > [ 3034.728033] #0: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8131e28a>] n_tty_read+0x252/0x7e8 > > Things looked a little weird. Also, this is a deadlock that lockdep did > not catch. But what we have here does not look like a circular lock > issue: > > Bash is blocked in rcu_cpu_notify(): > > 1961 /* Exclude any attempts to start a new grace period. */ > 1962 mutex_lock(&rsp->onoff_mutex); > > > kworker is blocked in get_online_cpus(), which makes sense as we are > currently taking down a CPU. > > But rcu_preempt is not blocked on anything. It is simply sleeping in > rcu_gp_kthread (really rcu_gp_init) here: > > 1453 #ifdef CONFIG_PROVE_RCU_DELAY > 1454 if ((prandom_u32() % (rcu_num_nodes * 8)) == 0 && > 1455 system_state == SYSTEM_RUNNING) > 1456 schedule_timeout_uninterruptible(2); > 1457 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ > > And it does this while holding the onoff_mutex that bash is waiting for. > > Doing a function trace, it showed me where it happened: > > [ 125.940066] rcu_pree-10 3.... 28384115273: schedule_timeout_uninterruptible <-rcu_gp_kthread > [...] > [ 125.940066] rcu_pree-10 3d..3 28384202439: sched_switch: prev_comm=rcu_preempt prev_pid=10 prev_prio=120 prev_state=D ==> next_comm=watchdog/3 next_pid=38 next_prio=120 > > The watchdog ran, and then: > > [ 125.940066] watchdog-38 3d..3 28384692863: sched_switch: prev_comm=watchdog/3 prev_pid=38 prev_prio=120 prev_state=P ==> next_comm=modprobe next_pid=2848 next_prio=118 > > Not sure what modprobe was doing, but shortly after that: > > [ 125.940066] modprobe-2848 3d..3 28385041749: sched_switch: prev_comm=modprobe prev_pid=2848 prev_prio=118 prev_state=R+ ==> next_comm=migration/3 next_pid=40 next_prio=0 > > Where the migration thread took down the CPU: > > [ 125.940066] migratio-40 3d..3 28389148276: sched_switch: prev_comm=migration/3 prev_pid=40 prev_prio=0 prev_state=P ==> next_comm=swapper/3 next_pid=0 next_prio=120 > > which finally did: > > [ 125.940066] <idle>-0 3...1 28389282142: arch_cpu_idle_dead <-cpu_startup_entry > [ 125.940066] <idle>-0 3...1 28389282548: native_play_dead <-arch_cpu_idle_dead > [ 125.940066] <idle>-0 3...1 28389282924: play_dead_common <-native_play_dead > [ 125.940066] <idle>-0 3...1 28389283468: idle_task_exit <-play_dead_common > [ 125.940066] <idle>-0 3...1 28389284644: amd_e400_remove_cpu <-play_dead_common > > > CPU 3 is now offline, the rcu_preempt thread that ran on CPU 3 is still > doing a schedule_timeout_uninterruptible() and it registered it's > timeout to the timer base for CPU 3. You would think that it would get > migrated right? The issue here is that the timer migration happens at > the CPU notifier for CPU_DEAD. The problem is that the rcu notifier for > CPU_DOWN is blocked waiting for the onoff_mutex to be released, which is > held by the thread that just put itself into a uninterruptible sleep, > that wont wake up until the CPU_DEAD notifier of the timer > infrastructure is called, which wont happen until the rcu notifier > finishes. Here's our deadlock! This commit breaks this deadlock cycle by substituting a shorter udelay() for the previous schedule_timeout_uninterruptible(), while at the same time increasing the probability of the delay. This maintains the intensity of the testing. Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Steven Rostedt <rostedt@goodmis.org>
2013-06-10rcu: Don't call wakeup() with rcu_node structure ->lock heldSteven Rostedt
This commit fixes a lockdep-detected deadlock by moving a wake_up() call out from a rnp->lock critical section. Please see below for the long version of this story. On Tue, 2013-05-28 at 16:13 -0400, Dave Jones wrote: > [12572.705832] ====================================================== > [12572.750317] [ INFO: possible circular locking dependency detected ] > [12572.796978] 3.10.0-rc3+ #39 Not tainted > [12572.833381] ------------------------------------------------------- > [12572.862233] trinity-child17/31341 is trying to acquire lock: > [12572.870390] (rcu_node_0){..-.-.}, at: [<ffffffff811054ff>] rcu_read_unlock_special+0x9f/0x4c0 > [12572.878859] > but task is already holding lock: > [12572.894894] (&ctx->lock){-.-...}, at: [<ffffffff811390ed>] perf_lock_task_context+0x7d/0x2d0 > [12572.903381] > which lock already depends on the new lock. > > [12572.927541] > the existing dependency chain (in reverse order) is: > [12572.943736] > -> #4 (&ctx->lock){-.-...}: > [12572.960032] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12572.968337] [<ffffffff816ebc90>] _raw_spin_lock+0x40/0x80 > [12572.976633] [<ffffffff8113c987>] __perf_event_task_sched_out+0x2e7/0x5e0 > [12572.984969] [<ffffffff81088953>] perf_event_task_sched_out+0x93/0xa0 > [12572.993326] [<ffffffff816ea0bf>] __schedule+0x2cf/0x9c0 > [12573.001652] [<ffffffff816eacfe>] schedule_user+0x2e/0x70 > [12573.009998] [<ffffffff816ecd64>] retint_careful+0x12/0x2e > [12573.018321] > -> #3 (&rq->lock){-.-.-.}: > [12573.034628] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12573.042930] [<ffffffff816ebc90>] _raw_spin_lock+0x40/0x80 > [12573.051248] [<ffffffff8108e6a7>] wake_up_new_task+0xb7/0x260 > [12573.059579] [<ffffffff810492f5>] do_fork+0x105/0x470 > [12573.067880] [<ffffffff81049686>] kernel_thread+0x26/0x30 > [12573.076202] [<ffffffff816cee63>] rest_init+0x23/0x140 > [12573.084508] [<ffffffff81ed8e1f>] start_kernel+0x3f1/0x3fe > [12573.092852] [<ffffffff81ed856f>] x86_64_start_reservations+0x2a/0x2c > [12573.101233] [<ffffffff81ed863d>] x86_64_start_kernel+0xcc/0xcf > [12573.109528] > -> #2 (&p->pi_lock){-.-.-.}: > [12573.125675] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12573.133829] [<ffffffff816ebe9b>] _raw_spin_lock_irqsave+0x4b/0x90 > [12573.141964] [<ffffffff8108e881>] try_to_wake_up+0x31/0x320 > [12573.150065] [<ffffffff8108ebe2>] default_wake_function+0x12/0x20 > [12573.158151] [<ffffffff8107bbf8>] autoremove_wake_function+0x18/0x40 > [12573.166195] [<ffffffff81085398>] __wake_up_common+0x58/0x90 > [12573.174215] [<ffffffff81086909>] __wake_up+0x39/0x50 > [12573.182146] [<ffffffff810fc3da>] rcu_start_gp_advanced.isra.11+0x4a/0x50 > [12573.190119] [<ffffffff810fdb09>] rcu_start_future_gp+0x1c9/0x1f0 > [12573.198023] [<ffffffff810fe2c4>] rcu_nocb_kthread+0x114/0x930 > [12573.205860] [<ffffffff8107a91d>] kthread+0xed/0x100 > [12573.213656] [<ffffffff816f4b1c>] ret_from_fork+0x7c/0xb0 > [12573.221379] > -> #1 (&rsp->gp_wq){..-.-.}: > [12573.236329] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12573.243783] [<ffffffff816ebe9b>] _raw_spin_lock_irqsave+0x4b/0x90 > [12573.251178] [<ffffffff810868f3>] __wake_up+0x23/0x50 > [12573.258505] [<ffffffff810fc3da>] rcu_start_gp_advanced.isra.11+0x4a/0x50 > [12573.265891] [<ffffffff810fdb09>] rcu_start_future_gp+0x1c9/0x1f0 > [12573.273248] [<ffffffff810fe2c4>] rcu_nocb_kthread+0x114/0x930 > [12573.280564] [<ffffffff8107a91d>] kthread+0xed/0x100 > [12573.287807] [<ffffffff816f4b1c>] ret_from_fork+0x7c/0xb0 Notice the above call chain. rcu_start_future_gp() is called with the rnp->lock held. Then it calls rcu_start_gp_advance, which does a wakeup. You can't do wakeups while holding the rnp->lock, as that would mean that you could not do a rcu_read_unlock() while holding the rq lock, or any lock that was taken while holding the rq lock. This is because... (See below). > [12573.295067] > -> #0 (rcu_node_0){..-.-.}: > [12573.309293] [<ffffffff810b8d36>] __lock_acquire+0x1786/0x1af0 > [12573.316568] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12573.323825] [<ffffffff816ebc90>] _raw_spin_lock+0x40/0x80 > [12573.331081] [<ffffffff811054ff>] rcu_read_unlock_special+0x9f/0x4c0 > [12573.338377] [<ffffffff810760a6>] __rcu_read_unlock+0x96/0xa0 > [12573.345648] [<ffffffff811391b3>] perf_lock_task_context+0x143/0x2d0 > [12573.352942] [<ffffffff8113938e>] find_get_context+0x4e/0x1f0 > [12573.360211] [<ffffffff811403f4>] SYSC_perf_event_open+0x514/0xbd0 > [12573.367514] [<ffffffff81140e49>] SyS_perf_event_open+0x9/0x10 > [12573.374816] [<ffffffff816f4dd4>] tracesys+0xdd/0xe2 Notice the above trace. perf took its own ctx->lock, which can be taken while holding the rq lock. While holding this lock, it did a rcu_read_unlock(). The perf_lock_task_context() basically looks like: rcu_read_lock(); raw_spin_lock(ctx->lock); rcu_read_unlock(); Now, what looks to have happened, is that we scheduled after taking that first rcu_read_lock() but before taking the spin lock. When we scheduled back in and took the ctx->lock, the following rcu_read_unlock() triggered the "special" code. The rcu_read_unlock_special() takes the rnp->lock, which gives us a possible deadlock scenario. CPU0 CPU1 CPU2 ---- ---- ---- rcu_nocb_kthread() lock(rq->lock); lock(ctx->lock); lock(rnp->lock); wake_up(); lock(rq->lock); rcu_read_unlock(); rcu_read_unlock_special(); lock(rnp->lock); lock(ctx->lock); **** DEADLOCK **** > [12573.382068] > other info that might help us debug this: > > [12573.403229] Chain exists of: > rcu_node_0 --> &rq->lock --> &ctx->lock > > [12573.424471] Possible unsafe locking scenario: > > [12573.438499] CPU0 CPU1 > [12573.445599] ---- ---- > [12573.452691] lock(&ctx->lock); > [12573.459799] lock(&rq->lock); > [12573.467010] lock(&ctx->lock); > [12573.474192] lock(rcu_node_0); > [12573.481262] > *** DEADLOCK *** > > [12573.501931] 1 lock held by trinity-child17/31341: > [12573.508990] #0: (&ctx->lock){-.-...}, at: [<ffffffff811390ed>] perf_lock_task_context+0x7d/0x2d0 > [12573.516475] > stack backtrace: > [12573.530395] CPU: 1 PID: 31341 Comm: trinity-child17 Not tainted 3.10.0-rc3+ #39 > [12573.545357] ffffffff825b4f90 ffff880219f1dbc0 ffffffff816e375b ffff880219f1dc00 > [12573.552868] ffffffff816dfa5d ffff880219f1dc50 ffff88023ce4d1f8 ffff88023ce4ca40 > [12573.560353] 0000000000000001 0000000000000001 ffff88023ce4d1f8 ffff880219f1dcc0 > [12573.567856] Call Trace: > [12573.575011] [<ffffffff816e375b>] dump_stack+0x19/0x1b > [12573.582284] [<ffffffff816dfa5d>] print_circular_bug+0x200/0x20f > [12573.589637] [<ffffffff810b8d36>] __lock_acquire+0x1786/0x1af0 > [12573.596982] [<ffffffff810918f5>] ? sched_clock_cpu+0xb5/0x100 > [12573.604344] [<ffffffff810b9851>] lock_acquire+0x91/0x1f0 > [12573.611652] [<ffffffff811054ff>] ? rcu_read_unlock_special+0x9f/0x4c0 > [12573.619030] [<ffffffff816ebc90>] _raw_spin_lock+0x40/0x80 > [12573.626331] [<ffffffff811054ff>] ? rcu_read_unlock_special+0x9f/0x4c0 > [12573.633671] [<ffffffff811054ff>] rcu_read_unlock_special+0x9f/0x4c0 > [12573.640992] [<ffffffff811390ed>] ? perf_lock_task_context+0x7d/0x2d0 > [12573.648330] [<ffffffff810b429e>] ? put_lock_stats.isra.29+0xe/0x40 > [12573.655662] [<ffffffff813095a0>] ? delay_tsc+0x90/0xe0 > [12573.662964] [<ffffffff810760a6>] __rcu_read_unlock+0x96/0xa0 > [12573.670276] [<ffffffff811391b3>] perf_lock_task_context+0x143/0x2d0 > [12573.677622] [<ffffffff81139070>] ? __perf_event_enable+0x370/0x370 > [12573.684981] [<ffffffff8113938e>] find_get_context+0x4e/0x1f0 > [12573.692358] [<ffffffff811403f4>] SYSC_perf_event_open+0x514/0xbd0 > [12573.699753] [<ffffffff8108cd9d>] ? get_parent_ip+0xd/0x50 > [12573.707135] [<ffffffff810b71fd>] ? trace_hardirqs_on_caller+0xfd/0x1c0 > [12573.714599] [<ffffffff81140e49>] SyS_perf_event_open+0x9/0x10 > [12573.721996] [<ffffffff816f4dd4>] tracesys+0xdd/0xe2 This commit delays the wakeup via irq_work(), which is what perf and ftrace use to perform wakeups in critical sections. Reported-by: Dave Jones <davej@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2013-05-02Merge commit '8700c95adb03' into timers/nohzFrederic Weisbecker
The full dynticks tree needs the latest RCU and sched upstream updates in order to fix some dependencies. Merge a common upstream merge point that has these updates. Conflicts: include/linux/perf_event.h kernel/rcutree.h kernel/rcutree_plugin.h Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
2013-04-30Merge branch 'core-rcu-for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull RCU updates from Ingo Molnar: "The main changes in this cycle are mostly related to preparatory work for the full-dynticks work: - Remove restrictions on no-CBs CPUs, make RCU_FAST_NO_HZ take advantage of numbered callbacks, do callback accelerations based on numbered callbacks. Posted to LKML at https://lkml.org/lkml/2013/3/18/960 - RCU documentation updates. Posted to LKML at https://lkml.org/lkml/2013/3/18/570 - Miscellaneous fixes. Posted to LKML at https://lkml.org/lkml/2013/3/18/594" * 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits) rcu: Make rcu_accelerate_cbs() note need for future grace periods rcu: Abstract rcu_start_future_gp() from rcu_nocb_wait_gp() rcu: Rename n_nocb_gp_requests to need_future_gp rcu: Push lock release to rcu_start_gp()'s callers rcu: Repurpose no-CBs event tracing to future-GP events rcu: Rearrange locking in rcu_start_gp() rcu: Make RCU_FAST_NO_HZ take advantage of numbered callbacks rcu: Accelerate RCU callbacks at grace-period end rcu: Export RCU_FAST_NO_HZ parameters to sysfs rcu: Distinguish "rcuo" kthreads by RCU flavor rcu: Add event tracing for no-CBs CPUs' grace periods rcu: Add event tracing for no-CBs CPUs' callback registration rcu: Introduce proper blocking to no-CBs kthreads GP waits rcu: Provide compile-time control for no-CBs CPUs rcu: Tone down debugging during boot-up and shutdown. rcu: Add softirq-stall indications to stall-warning messages rcu: Documentation update rcu: Make bugginess of code sample more evident rcu: Fix hlist_bl_set_first_rcu() annotation rcu: Delete unused rcu_node "wakemask" field ...
2013-04-29kernel/: rename random32() to prandom_u32()Akinobu Mita
Use preferable function name which implies using a pseudo-random number generator. Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>