From 551d55a944b143ef26fbd482d1c463199d6f65cf Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Sat, 17 Apr 2010 08:48:42 -0400 Subject: tree/tiny rcu: Add debug RCU head objects Helps finding racy users of call_rcu(), which results in hangs because list entries are overwritten and/or skipped. Changelog since v4: - Bissectability is now OK - Now generate a WARN_ON_ONCE() for non-initialized rcu_head passed to call_rcu(). Statically initialized objects are detected with object_is_static(). - Rename rcu_head_init_on_stack to init_rcu_head_on_stack. - Remove init_rcu_head() completely. Changelog since v3: - Include comments from Lai Jiangshan This new patch version is based on the debugobjects with the newly introduced "active state" tracker. Non-initialized entries are all considered as "statically initialized". An activation fixup (triggered by call_rcu()) takes care of performing the debug object initialization without issuing any warning. Since we cannot increase the size of struct rcu_head, I don't see much room to put an identifier for statically initialized rcu_head structures. So for now, we have to live without "activation without explicit init" detection. But the main purpose of this debug option is to detect double-activations (double call_rcu() use of a rcu_head before the callback is executed), which is correctly addressed here. This also detects potential internal RCU callback corruption, which would cause the callbacks to be executed twice. Signed-off-by: Mathieu Desnoyers CC: David S. Miller CC: "Paul E. McKenney" CC: akpm@linux-foundation.org CC: mingo@elte.hu CC: laijs@cn.fujitsu.com CC: dipankar@in.ibm.com CC: josh@joshtriplett.org CC: dvhltc@us.ibm.com CC: niv@us.ibm.com CC: tglx@linutronix.de CC: peterz@infradead.org CC: rostedt@goodmis.org CC: Valdis.Kletnieks@vt.edu CC: dhowells@redhat.com CC: eric.dumazet@gmail.com CC: Alexey Dobriyan Signed-off-by: Paul E. McKenney Reviewed-by: Lai Jiangshan --- kernel/rcupdate.c | 160 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 160 insertions(+) (limited to 'kernel/rcupdate.c') diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 72a8dc9567f..4d169835fb3 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -114,3 +114,163 @@ int rcu_my_thread_group_empty(void) } EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty); #endif /* #ifdef CONFIG_PROVE_RCU */ + +#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD +static inline void debug_init_rcu_head(struct rcu_head *head) +{ + debug_object_init(head, &rcuhead_debug_descr); +} + +static inline void debug_rcu_head_free(struct rcu_head *head) +{ + debug_object_free(head, &rcuhead_debug_descr); +} + +/* + * fixup_init is called when: + * - an active object is initialized + */ +static int rcuhead_fixup_init(void *addr, enum debug_obj_state state) +{ + struct rcu_head *head = addr; + + switch (state) { + case ODEBUG_STATE_ACTIVE: + /* + * Ensure that queued callbacks are all executed. + * If we detect that we are nested in a RCU read-side critical + * section, we should simply fail, otherwise we would deadlock. + */ + if (rcu_preempt_depth() != 0 || preempt_count() != 0 || + irqs_disabled()) { + WARN_ON(1); + return 0; + } + rcu_barrier(); + rcu_barrier_sched(); + rcu_barrier_bh(); + debug_object_init(head, &rcuhead_debug_descr); + return 1; + default: + return 0; + } +} + +/* + * fixup_activate is called when: + * - an active object is activated + * - an unknown object is activated (might be a statically initialized object) + * Activation is performed internally by call_rcu(). + */ +static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) +{ + struct rcu_head *head = addr; + + switch (state) { + + case ODEBUG_STATE_NOTAVAILABLE: + /* + * This is not really a fixup. We just make sure that it is + * tracked in the object tracker. + */ + debug_object_init(head, &rcuhead_debug_descr); + debug_object_activate(head, &rcuhead_debug_descr); + return 0; + + case ODEBUG_STATE_ACTIVE: + /* + * Ensure that queued callbacks are all executed. + * If we detect that we are nested in a RCU read-side critical + * section, we should simply fail, otherwise we would deadlock. + */ + if (rcu_preempt_depth() != 0 || preempt_count() != 0 || + irqs_disabled()) { + WARN_ON(1); + return 0; + } + rcu_barrier(); + rcu_barrier_sched(); + rcu_barrier_bh(); + debug_object_activate(head, &rcuhead_debug_descr); + return 1; + default: + return 0; + } +} + +/* + * fixup_free is called when: + * - an active object is freed + */ +static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) +{ + struct rcu_head *head = addr; + + switch (state) { + case ODEBUG_STATE_ACTIVE: + /* + * Ensure that queued callbacks are all executed. + * If we detect that we are nested in a RCU read-side critical + * section, we should simply fail, otherwise we would deadlock. + */ +#ifndef CONFIG_PREEMPT + WARN_ON(1); + return 0; +#else + if (rcu_preempt_depth() != 0 || preempt_count() != 0 || + irqs_disabled()) { + WARN_ON(1); + return 0; + } + rcu_barrier(); + rcu_barrier_sched(); + rcu_barrier_bh(); + debug_object_free(head, &rcuhead_debug_descr); + return 1; +#endif + default: + return 0; + } +} + +/** + * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects + * @head: pointer to rcu_head structure to be initialized + * + * This function informs debugobjects of a new rcu_head structure that + * has been allocated as an auto variable on the stack. This function + * is not required for rcu_head structures that are statically defined or + * that are dynamically allocated on the heap. This function has no + * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. + */ +void init_rcu_head_on_stack(struct rcu_head *head) +{ + debug_object_init_on_stack(head, &rcuhead_debug_descr); +} +EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); + +/** + * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects + * @head: pointer to rcu_head structure to be initialized + * + * This function informs debugobjects that an on-stack rcu_head structure + * is about to go out of scope. As with init_rcu_head_on_stack(), this + * function is not required for rcu_head structures that are statically + * defined or that are dynamically allocated on the heap. Also as with + * init_rcu_head_on_stack(), this function has no effect for + * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. + */ +void destroy_rcu_head_on_stack(struct rcu_head *head) +{ + debug_object_free(head, &rcuhead_debug_descr); +} +EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); + +struct debug_obj_descr rcuhead_debug_descr = { + .name = "rcu_head", + .fixup_init = rcuhead_fixup_init, + .fixup_activate = rcuhead_fixup_activate, + .fixup_free = rcuhead_fixup_free, +}; +EXPORT_SYMBOL_GPL(rcuhead_debug_descr); +#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ -- cgit v1.2.3-70-g09d2