From 3660c2813fb6d0ba48ee44bcbf9feddf7218c11d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 3 Dec 2013 09:24:02 -0800 Subject: rcu: Add ACCESS_ONCE() to ->n_force_qs_lh accesses The ->n_force_qs_lh field is accessed without the benefit of any synchronization, so this commit adds the needed ACCESS_ONCE() wrappers. Yes, increments to ->n_force_qs_lh can be lost, but contention should be low and the field is strictly statistical in nature, so this is not a problem. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcu/tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index b3d116cd072..e6415779862 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2304,7 +2304,7 @@ static void force_quiescent_state(struct rcu_state *rsp) if (rnp_old != NULL) raw_spin_unlock(&rnp_old->fqslock); if (ret) { - rsp->n_force_qs_lh++; + ACCESS_ONCE(rsp->n_force_qs_lh)++; return; } rnp_old = rnp; @@ -2316,7 +2316,7 @@ static void force_quiescent_state(struct rcu_state *rsp) smp_mb__after_unlock_lock(); raw_spin_unlock(&rnp_old->fqslock); if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) { - rsp->n_force_qs_lh++; + ACCESS_ONCE(rsp->n_force_qs_lh)++; raw_spin_unlock_irqrestore(&rnp_old->lock, flags); return; /* Someone beat us to it. */ } -- cgit v1.2.3-70-g09d2 From 87de1cfdc55b16b794e245b07322340725149d62 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 3 Dec 2013 10:02:52 -0800 Subject: rcu: Stop tracking FSF's postal address All of the RCU source files have the usual GPL header, which contains a long-obsolete postal address for FSF. To avoid the need to track the FSF office's movements, this commit substitutes the URL where GPL may be found. Reported-by: Greg KH Reported-by: Steven Rostedt Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 4 ++-- include/linux/rcutiny.h | 4 ++-- include/linux/rcutree.h | 4 ++-- include/linux/srcu.h | 4 ++-- kernel/rcu/rcu.h | 4 ++-- kernel/rcu/srcu.c | 4 ++-- kernel/rcu/tiny.c | 4 ++-- kernel/rcu/tiny_plugin.h | 4 ++-- kernel/rcu/torture.c | 4 ++-- kernel/rcu/tree.c | 4 ++-- kernel/rcu/tree.h | 4 ++-- kernel/rcu/tree_plugin.h | 4 ++-- kernel/rcu/tree_trace.c | 4 ++-- kernel/rcu/update.c | 4 ++-- 14 files changed, 28 insertions(+), 28 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 72bf3a01a4e..b200756ea4c 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2001 * diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 6f01771b571..c364e9148de 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2008 * diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 72137ee8c60..08b08406896 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2008 * diff --git a/include/linux/srcu.h b/include/linux/srcu.h index 9b058eecd40..a2783cb5d27 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright (C) IBM Corporation, 2006 * Copyright (C) Fujitsu, 2012 diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 79c3877e9c5..1bd787fddcb 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2011 * diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c index 3318d828438..5db7e9272d3 100644 --- a/kernel/rcu/srcu.c +++ b/kernel/rcu/srcu.c @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright (C) IBM Corporation, 2006 * Copyright (C) Fujitsu, 2012 diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index 1254f312d02..53b95bbf4ab 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2008 * diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h index 280d06cae35..43152852056 100644 --- a/kernel/rcu/tiny_plugin.h +++ b/kernel/rcu/tiny_plugin.h @@ -14,8 +14,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright (c) 2010 Linaro * diff --git a/kernel/rcu/torture.c b/kernel/rcu/torture.c index 732f8ae3086..ab7dd192a50 100644 --- a/kernel/rcu/torture.c +++ b/kernel/rcu/torture.c @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright (C) IBM Corporation, 2005, 2006 * diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e6415779862..321feef0f5c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2008 * diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 8c19873f1ac..75dc3c39a02 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -13,8 +13,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2008 * diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 6e2ef4b2b92..f9b9cdd36c8 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -14,8 +14,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright Red Hat, 2009 * Copyright IBM Corporation, 2009 diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c index d1f1e64a6d7..5cdc62e1bee 100644 --- a/kernel/rcu/tree_trace.c +++ b/kernel/rcu/tree_trace.c @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2008 * diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index c54609faf23..fd0d5b5b8e7 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -12,8 +12,8 @@ * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * along with this program; if not, you can access it online at + * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2001 * -- cgit v1.2.3-70-g09d2 From cb1e78cfa267453bb19e7edafd214c03834b664c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 4 Dec 2013 18:42:03 -0800 Subject: rcu: Remove ACCESS_ONCE() from jiffies Because jiffies is one of a very few variables marked "volatile", there is no need to use ACCESS_ONCE() when accessing it. This commit therefore removes the redundant ACCESS_ONCE() wrappers. Reported by: Eric Dumazet Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcu/torture.c | 4 ++-- kernel/rcu/tree.c | 6 +++--- 2 files changed, 5 insertions(+), 5 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/torture.c b/kernel/rcu/torture.c index ab7dd192a50..022c5312b72 100644 --- a/kernel/rcu/torture.c +++ b/kernel/rcu/torture.c @@ -1352,7 +1352,7 @@ rcu_torture_shutdown(void *arg) unsigned long jiffies_snap; VERBOSE_PRINTK_STRING("rcu_torture_shutdown task started"); - jiffies_snap = ACCESS_ONCE(jiffies); + jiffies_snap = jiffies; while (ULONG_CMP_LT(jiffies_snap, shutdown_time) && !kthread_should_stop()) { delta = shutdown_time - jiffies_snap; @@ -1361,7 +1361,7 @@ rcu_torture_shutdown(void *arg) "rcu_torture_shutdown task: %lu jiffies remaining\n", torture_type, delta); schedule_timeout_interruptible(delta); - jiffies_snap = ACCESS_ONCE(jiffies); + jiffies_snap = jiffies; } if (kthread_should_stop()) { VERBOSE_PRINTK_STRING("rcu_torture_shutdown task stopping"); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 321feef0f5c..73c3cd2b87a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -837,7 +837,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, * to the next. Only do this for the primary flavor of RCU. */ if (rdp->rsp == rcu_state && - ULONG_CMP_GE(ACCESS_ONCE(jiffies), rdp->rsp->jiffies_resched)) { + ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) { rdp->rsp->jiffies_resched += 5; resched_cpu(rdp->cpu); } @@ -847,7 +847,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, static void record_gp_stall_check_time(struct rcu_state *rsp) { - unsigned long j = ACCESS_ONCE(jiffies); + unsigned long j = jiffies; unsigned long j1; rsp->gp_start = j; @@ -1005,7 +1005,7 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp)) return; - j = ACCESS_ONCE(jiffies); + j = jiffies; /* * Lots of memory barriers to reject false positives. -- cgit v1.2.3-70-g09d2 From ffa83fb565fbc397cbafb4b71fd1cce276d4c3b6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 17 Nov 2013 19:27:16 -0800 Subject: rcu: Optimize rcu_needs_cpu() for RCU_NOCB_CPU_ALL If CONFIG_RCU_NOCB_CPU_ALL=y, then rcu_needs_cpu() will always return false, however, the current version nevertheless checks for RCU callbacks. This commit therefore creates a static inline implementation of rcu_needs_cpu() that unconditionally returns false when CONFIG_RCU_NOCB_CPU_ALL=y. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 8 ++++++++ include/linux/rcutiny.h | 6 ------ include/linux/rcutree.h | 2 ++ kernel/rcu/tree.c | 2 +- kernel/rcu/tree_plugin.h | 4 ++++ 5 files changed, 15 insertions(+), 7 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 281c90f8989..5f7d5f410d5 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -1015,6 +1015,14 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) #define kfree_rcu(ptr, rcu_head) \ __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) +#if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) +static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) +{ + *delta_jiffies = ULONG_MAX; + return 0; +} +#endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */ + #if defined(CONFIG_RCU_NOCB_CPU_ALL) static inline bool rcu_is_nocb_cpu(int cpu) { return true; } #elif defined(CONFIG_RCU_NOCB_CPU) diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 6f01771b571..9524903487d 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -68,12 +68,6 @@ static inline void kfree_call_rcu(struct rcu_head *head, call_rcu(head, func); } -static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) -{ - *delta_jiffies = ULONG_MAX; - return 0; -} - static inline void rcu_note_context_switch(int cpu) { rcu_sched_qs(cpu); diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 72137ee8c60..81198c84e26 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -31,7 +31,9 @@ #define __LINUX_RCUTREE_H void rcu_note_context_switch(int cpu); +#ifndef CONFIG_RCU_NOCB_CPU_ALL int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies); +#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ void rcu_cpu_stall_reset(void); /* diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index b3d116cd072..c2c8234a029 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2880,7 +2880,7 @@ static int rcu_pending(int cpu) * non-NULL, store an indication of whether all callbacks are lazy. * (If there are no callbacks, all of them are deemed to be lazy.) */ -static int rcu_cpu_has_callbacks(int cpu, bool *all_lazy) +static int __maybe_unused rcu_cpu_has_callbacks(int cpu, bool *all_lazy) { bool al = true; bool hc = false; diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 39a50b918bf..820b06aefbe 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1586,11 +1586,13 @@ static void rcu_prepare_kthreads(int cpu) * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs * any flavor of RCU. */ +#ifndef CONFIG_RCU_NOCB_CPU_ALL int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) { *delta_jiffies = ULONG_MAX; return rcu_cpu_has_callbacks(cpu, NULL); } +#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ /* * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up @@ -1696,6 +1698,7 @@ static bool rcu_try_advance_all_cbs(void) * * The caller must have disabled interrupts. */ +#ifndef CONFIG_RCU_NOCB_CPU_ALL int rcu_needs_cpu(int cpu, unsigned long *dj) { struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); @@ -1726,6 +1729,7 @@ int rcu_needs_cpu(int cpu, unsigned long *dj) } return 0; } +#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ /* * Prepare a CPU for idle from an RCU perspective. The first major task -- cgit v1.2.3-70-g09d2 From 5cb5c6e18f822b19bd41a2c0f9930c82b3ec0bc9 Mon Sep 17 00:00:00 2001 From: Paul Gortmaker Date: Wed, 19 Feb 2014 14:33:27 -0500 Subject: rcu: Ensure kernel/rcu/rcu.h can be sourced/used stand-alone The kbuild test bot uncovered an implicit dependence on the trace header being present before rcu.h in ia64 allmodconfig that looks like this: In file included from kernel/ksysfs.c:22:0: kernel/rcu/rcu.h: In function '__rcu_reclaim': kernel/rcu/rcu.h:107:3: error: implicit declaration of function 'trace_rcu_invoke_kfree_callback' [-Werror=implicit-function-declaration] kernel/rcu/rcu.h:112:3: error: implicit declaration of function 'trace_rcu_invoke_callback' [-Werror=implicit-function-declaration] cc1: some warnings being treated as errors Looking at other rcu.h users, we can find that they all were sourcing the trace header in advance of rcu.h itself, as seen in the context of this diff. There were also some inconsistencies as to whether it was or wasn't sourced based on the parent tracing Kconfig. Rather than "fix" it at each use site, and have inconsistent use based on whether "#ifdef CONFIG_RCU_TRACE" was used or not, lets just source the trace header just once, in the actual consumer of it, which is rcu.h itself. We include it unconditionally, as build testing shows us that is a hard requirement for some files. Reported-by: kbuild test robot Signed-off-by: Paul Gortmaker Signed-off-by: Paul E. McKenney --- kernel/rcu/rcu.h | 1 + kernel/rcu/srcu.c | 2 -- kernel/rcu/tiny.c | 4 ---- kernel/rcu/tree.c | 2 -- kernel/rcu/update.c | 1 - 5 files changed, 1 insertion(+), 9 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index af2e60a8425..bfda2726ca4 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -23,6 +23,7 @@ #ifndef __LINUX_RCU_H #define __LINUX_RCU_H +#include #ifdef CONFIG_RCU_TRACE #define RCU_TRACE(stmt) stmt #else /* #ifdef CONFIG_RCU_TRACE */ diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c index 2359779e1da..c639556f3fa 100644 --- a/kernel/rcu/srcu.c +++ b/kernel/rcu/srcu.c @@ -36,8 +36,6 @@ #include #include -#include - #include "rcu.h" /* diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index 53b95bbf4ab..d9efcc13008 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -37,10 +37,6 @@ #include #include -#ifdef CONFIG_RCU_TRACE -#include -#endif /* #else #ifdef CONFIG_RCU_TRACE */ - #include "rcu.h" /* Forward declarations for tiny_plugin.h. */ diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 73c3cd2b87a..c7ed5db2dd7 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -58,8 +58,6 @@ #include #include "tree.h" -#include - #include "rcu.h" MODULE_ALIAS("rcutree"); diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index fd0d5b5b8e7..4c0a9b0af46 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -49,7 +49,6 @@ #include #define CREATE_TRACE_POINTS -#include #include "rcu.h" -- cgit v1.2.3-70-g09d2 From 765a3f4fed708ae429ee095914a7897acb3a65bd Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 14 Mar 2014 16:37:08 -0700 Subject: rcu: Provide grace-period piggybacking API The following pattern is currently not well supported by RCU: 1. Make data element inaccessible to RCU readers. 2. Do work that probably lasts for more than one grace period. 3. Do something to make sure RCU readers in flight before #1 above have completed. Here are some things that could currently be done: a. Do a synchronize_rcu() unconditionally at either #1 or #3 above. This works, but imposes needless work and latency. b. Post an RCU callback at #1 above that does a wakeup, then wait for the wakeup at #3. This works well, but likely results in an extra unneeded grace period. Open-coding this is also a bit more semi-tricky code than would be good. This commit therefore adds get_state_synchronize_rcu() and cond_synchronize_rcu() APIs. Call get_state_synchronize_rcu() at #1 above and pass its return value to cond_synchronize_rcu() at #3 above. This results in a call to synchronize_rcu() if no grace period has elapsed between #1 and #3, but requires only a load, comparison, and memory barrier if a full grace period did elapse. Requested-by: Peter Zijlstra Signed-off-by: Paul E. McKenney Acked-by: Peter Zijlstra --- include/linux/rcutiny.h | 10 ++++++++ include/linux/rcutree.h | 2 ++ kernel/rcu/tree.c | 62 +++++++++++++++++++++++++++++++++++++++++++++---- 3 files changed, 70 insertions(+), 4 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index e8cb6e3b52a..425c659d54e 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -27,6 +27,16 @@ #include +static inline unsigned long get_state_synchronize_rcu(void) +{ + return 0; +} + +static inline void cond_synchronize_rcu(unsigned long oldstate) +{ + might_sleep(); +} + static inline void rcu_barrier_bh(void) { wait_rcu_gp(call_rcu_bh); diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index e9c63884df0..a59ca05fd4e 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -76,6 +76,8 @@ static inline void synchronize_rcu_bh_expedited(void) void rcu_barrier(void); void rcu_barrier_bh(void); void rcu_barrier_sched(void); +unsigned long get_state_synchronize_rcu(void); +void cond_synchronize_rcu(unsigned long oldstate); extern unsigned long rcutorture_testseq; extern unsigned long rcutorture_vernum; diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 351faba48b9..0c47e300210 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1421,13 +1421,14 @@ static int rcu_gp_init(struct rcu_state *rsp) /* Advance to a new grace period and initialize state. */ record_gp_stall_check_time(rsp); - smp_wmb(); /* Record GP times before starting GP. */ - rsp->gpnum++; + /* Record GP times before starting GP, hence smp_store_release(). */ + smp_store_release(&rsp->gpnum, rsp->gpnum + 1); trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start")); raw_spin_unlock_irq(&rnp->lock); /* Exclude any concurrent CPU-hotplug operations. */ mutex_lock(&rsp->onoff_mutex); + smp_mb__after_unlock_lock(); /* ->gpnum increment before GP! */ /* * Set the quiescent-state-needed bits in all the rcu_node @@ -1555,10 +1556,11 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) } rnp = rcu_get_root(rsp); raw_spin_lock_irq(&rnp->lock); - smp_mb__after_unlock_lock(); + smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */ rcu_nocb_gp_set(rnp, nocb); - rsp->completed = rsp->gpnum; /* Declare grace period done. */ + /* Declare grace period done. */ + ACCESS_ONCE(rsp->completed) = rsp->gpnum; trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end")); rsp->fqs_state = RCU_GP_IDLE; rdp = this_cpu_ptr(rsp->rda); @@ -2637,6 +2639,58 @@ void synchronize_rcu_bh(void) } EXPORT_SYMBOL_GPL(synchronize_rcu_bh); +/** + * get_state_synchronize_rcu - Snapshot current RCU state + * + * Returns a cookie that is used by a later call to cond_synchronize_rcu() + * to determine whether or not a full grace period has elapsed in the + * meantime. + */ +unsigned long get_state_synchronize_rcu(void) +{ + /* + * Any prior manipulation of RCU-protected data must happen + * before the load from ->gpnum. + */ + smp_mb(); /* ^^^ */ + + /* + * Make sure this load happens before the purportedly + * time-consuming work between get_state_synchronize_rcu() + * and cond_synchronize_rcu(). + */ + return smp_load_acquire(&rcu_state->gpnum); +} +EXPORT_SYMBOL_GPL(get_state_synchronize_rcu); + +/** + * cond_synchronize_rcu - Conditionally wait for an RCU grace period + * + * @oldstate: return value from earlier call to get_state_synchronize_rcu() + * + * If a full RCU grace period has elapsed since the earlier call to + * get_state_synchronize_rcu(), just return. Otherwise, invoke + * synchronize_rcu() to wait for a full grace period. + * + * Yes, this function does not take counter wrap into account. But + * counter wrap is harmless. If the counter wraps, we have waited for + * more than 2 billion grace periods (and way more on a 64-bit system!), + * so waiting for one additional grace period should be just fine. + */ +void cond_synchronize_rcu(unsigned long oldstate) +{ + unsigned long newstate; + + /* + * Ensure that this load happens before any RCU-destructive + * actions the caller might carry out after we return. + */ + newstate = smp_load_acquire(&rcu_state->completed); + if (ULONG_CMP_GE(oldstate, newstate)) + synchronize_rcu(); +} +EXPORT_SYMBOL_GPL(cond_synchronize_rcu); + static int synchronize_sched_expedited_cpu_stop(void *data) { /* -- cgit v1.2.3-70-g09d2