From 9b2e4f1880b789be1f24f9684f7a54b90310b5c0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 30 Sep 2011 12:10:22 -0700 Subject: rcu: Track idleness independent of idle tasks Earlier versions of RCU used the scheduling-clock tick to detect idleness by checking for the idle task, but handled idleness differently for CONFIG_NO_HZ=y. But there are now a number of uses of RCU read-side critical sections in the idle task, for example, for tracing. A more fine-grained detection of idleness is therefore required. This commit presses the old dyntick-idle code into full-time service, so that rcu_idle_enter(), previously known as rcu_enter_nohz(), is always invoked at the beginning of an idle loop iteration. Similarly, rcu_idle_exit(), previously known as rcu_exit_nohz(), is always invoked at the end of an idle-loop iteration. This allows the idle task to use RCU everywhere except between consecutive rcu_idle_enter() and rcu_idle_exit() calls, in turn allowing architecture maintainers to specify exactly where in the idle loop that RCU may be used. Because some of the userspace upcall uses can result in what looks to RCU like half of an interrupt, it is not possible to expect that the irq_enter() and irq_exit() hooks will give exact counts. This patch therefore expands the ->dynticks_nesting counter to 64 bits and uses two separate bitfields to count process/idle transitions and interrupt entry/exit transitions. It is presumed that userspace upcalls do not happen in the idle loop or from usermode execution (though usermode might do a system call that results in an upcall). The counter is hard-reset on each process/idle transition, which avoids the interrupt entry/exit error from accumulating. Overflow is avoided by the 64-bitness of the ->dyntick_nesting counter. This commit also adds warnings if a non-idle task asks RCU to enter idle state (and these checks will need some adjustment before applying Frederic's OS-jitter patches (http://lkml.org/lkml/2011/10/7/246). In addition, validation of ->dynticks and ->dynticks_nesting is added. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 21 ++++----------------- 1 file changed, 4 insertions(+), 17 deletions(-) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 2cf4226ade7e..cd1ad4b04c6d 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -177,23 +177,10 @@ extern void rcu_sched_qs(int cpu); extern void rcu_bh_qs(int cpu); extern void rcu_check_callbacks(int cpu, int user); struct notifier_block; - -#ifdef CONFIG_NO_HZ - -extern void rcu_enter_nohz(void); -extern void rcu_exit_nohz(void); - -#else /* #ifdef CONFIG_NO_HZ */ - -static inline void rcu_enter_nohz(void) -{ -} - -static inline void rcu_exit_nohz(void) -{ -} - -#endif /* #else #ifdef CONFIG_NO_HZ */ +extern void rcu_idle_enter(void); +extern void rcu_idle_exit(void); +extern void rcu_irq_enter(void); +extern void rcu_irq_exit(void); /* * Infrastructure to implement the synchronize_() primitives in -- cgit From 91afaf300269aa99a4d646969b3258b74294ac4d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 2 Oct 2011 07:44:32 -0700 Subject: rcu: Add failure tracing to rcutorture Trace the rcutorture RCU accesses and dump the trace buffer when the first failure is detected. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 8 ++++++++ include/trace/events/rcu.h | 26 ++++++++++++++++++++++++++ kernel/rcupdate.c | 10 ++++++++++ kernel/rcutorture.c | 18 ++++++++++++++++++ 4 files changed, 62 insertions(+) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index cd1ad4b04c6d..8d315b013e37 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -51,6 +51,8 @@ extern int rcutorture_runnable; /* for sysctl */ #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) extern void rcutorture_record_test_transition(void); extern void rcutorture_record_progress(unsigned long vernum); +extern void do_trace_rcu_torture_read(char *rcutorturename, + struct rcu_head *rhp); #else static inline void rcutorture_record_test_transition(void) { @@ -58,6 +60,12 @@ static inline void rcutorture_record_test_transition(void) static inline void rcutorture_record_progress(unsigned long vernum) { } +#ifdef CONFIG_RCU_TRACE +extern void do_trace_rcu_torture_read(char *rcutorturename, + struct rcu_head *rhp); +#else +#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0) +#endif #endif #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index e5771804c507..172620a92b1a 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -437,6 +437,31 @@ TRACE_EVENT(rcu_batch_end, __entry->rcuname, __entry->callbacks_invoked) ); +/* + * Tracepoint for rcutorture readers. The first argument is the name + * of the RCU flavor from rcutorture's viewpoint and the second argument + * is the callback address. + */ +TRACE_EVENT(rcu_torture_read, + + TP_PROTO(char *rcutorturename, struct rcu_head *rhp), + + TP_ARGS(rcutorturename, rhp), + + TP_STRUCT__entry( + __field(char *, rcutorturename) + __field(struct rcu_head *, rhp) + ), + + TP_fast_assign( + __entry->rcutorturename = rcutorturename; + __entry->rhp = rhp; + ), + + TP_printk("%s torture read %p", + __entry->rcutorturename, __entry->rhp) +); + #else /* #ifdef CONFIG_RCU_TRACE */ #define trace_rcu_grace_period(rcuname, gpnum, gpevent) do { } while (0) @@ -452,6 +477,7 @@ TRACE_EVENT(rcu_batch_end, #define trace_rcu_invoke_callback(rcuname, rhp) do { } while (0) #define trace_rcu_invoke_kfree_callback(rcuname, rhp, offset) do { } while (0) #define trace_rcu_batch_end(rcuname, callbacks_invoked) do { } while (0) +#define trace_rcu_torture_read(rcutorturename, rhp) do { } while (0) #endif /* #else #ifdef CONFIG_RCU_TRACE */ diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index c5b98e565aee..92e771d7b44b 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -316,3 +316,13 @@ struct debug_obj_descr rcuhead_debug_descr = { }; EXPORT_SYMBOL_GPL(rcuhead_debug_descr); #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ + +#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE) +void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp) +{ + trace_rcu_torture_read(rcutorturename, rhp); +} +EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); +#else +#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0) +#endif diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 764825c2685c..df35228e743b 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -913,6 +913,18 @@ rcu_torture_fakewriter(void *arg) return 0; } +void rcutorture_trace_dump(void) +{ + static atomic_t beenhere = ATOMIC_INIT(0); + + if (atomic_read(&beenhere)) + return; + if (atomic_xchg(&beenhere, 1) != 0) + return; + do_trace_rcu_torture_read(cur_ops->name, (struct rcu_head *)~0UL); + ftrace_dump(DUMP_ALL); +} + /* * RCU torture reader from timer handler. Dereferences rcu_torture_current, * incrementing the corresponding element of the pipeline array. The @@ -934,6 +946,7 @@ static void rcu_torture_timer(unsigned long unused) rcu_read_lock_bh_held() || rcu_read_lock_sched_held() || srcu_read_lock_held(&srcu_ctl)); + do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu); if (p == NULL) { /* Leave because rcu_torture_writer is not yet underway */ cur_ops->readunlock(idx); @@ -951,6 +964,8 @@ static void rcu_torture_timer(unsigned long unused) /* Should not happen, but... */ pipe_count = RCU_TORTURE_PIPE_LEN; } + if (pipe_count > 1) + rcutorture_trace_dump(); __this_cpu_inc(rcu_torture_count[pipe_count]); completed = cur_ops->completed() - completed; if (completed > RCU_TORTURE_PIPE_LEN) { @@ -994,6 +1009,7 @@ rcu_torture_reader(void *arg) rcu_read_lock_bh_held() || rcu_read_lock_sched_held() || srcu_read_lock_held(&srcu_ctl)); + do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu); if (p == NULL) { /* Wait for rcu_torture_writer to get underway */ cur_ops->readunlock(idx); @@ -1009,6 +1025,8 @@ rcu_torture_reader(void *arg) /* Should not happen, but... */ pipe_count = RCU_TORTURE_PIPE_LEN; } + if (pipe_count > 1) + rcutorture_trace_dump(); __this_cpu_inc(rcu_torture_count[pipe_count]); completed = cur_ops->completed() - completed; if (completed > RCU_TORTURE_PIPE_LEN) { -- cgit From e6b80a3b0994ea6c3d876d72464f2debbfcfeb05 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 7 Oct 2011 16:25:18 -0700 Subject: rcu: Detect illegal rcu dereference in extended quiescent state Report that none of the rcu read lock maps are held while in an RCU extended quiescent state (the section between rcu_idle_enter() and rcu_idle_exit()). This helps detect any use of rcu_dereference() and friends from within the section in idle where RCU is not allowed. This way we can guarantee an extended quiescent window where the CPU can be put in dyntick idle mode or can simply aoid to be part of any global grace period completion while in the idle loop. Uses of RCU from such mode are totally ignored by RCU, hence the importance of these checks. Signed-off-by: Frederic Weisbecker Cc: Paul E. McKenney Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Lai Jiangshan Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 26 ++++++++++++++++++++++++++ kernel/rcupdate.c | 2 ++ kernel/rcutiny.c | 1 + kernel/rcutree.c | 1 + 4 files changed, 30 insertions(+) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 8d315b013e37..bf91fcfe181c 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -228,6 +228,15 @@ static inline void destroy_rcu_head_on_stack(struct rcu_head *head) #ifdef CONFIG_DEBUG_LOCK_ALLOC +#ifdef CONFIG_PROVE_RCU +extern int rcu_is_cpu_idle(void); +#else /* !CONFIG_PROVE_RCU */ +static inline int rcu_is_cpu_idle(void) +{ + return 0; +} +#endif /* else !CONFIG_PROVE_RCU */ + extern struct lockdep_map rcu_lock_map; # define rcu_read_acquire() \ lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) @@ -262,6 +271,8 @@ static inline int rcu_read_lock_held(void) { if (!debug_lockdep_rcu_enabled()) return 1; + if (rcu_is_cpu_idle()) + return 0; return lock_is_held(&rcu_lock_map); } @@ -285,6 +296,19 @@ extern int rcu_read_lock_bh_held(void); * * Check debug_lockdep_rcu_enabled() to prevent false positives during boot * and while lockdep is disabled. + * + * Note that if the CPU is in the idle loop from an RCU point of + * view (ie: that we are in the section between rcu_idle_enter() and + * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU + * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs + * that are in such a section, considering these as in extended quiescent + * state, so such a CPU is effectively never in an RCU read-side critical + * section regardless of what RCU primitives it invokes. This state of + * affairs is required --- we need to keep an RCU-free window in idle + * where the CPU may possibly enter into low power mode. This way we can + * notice an extended quiescent state to other CPUs that started a grace + * period. Otherwise we would delay any grace period as long as we run in + * the idle task. */ #ifdef CONFIG_PREEMPT_COUNT static inline int rcu_read_lock_sched_held(void) @@ -293,6 +317,8 @@ static inline int rcu_read_lock_sched_held(void) if (!debug_lockdep_rcu_enabled()) return 1; + if (rcu_is_cpu_idle()) + return 0; if (debug_locks) lockdep_opinion = lock_is_held(&rcu_sched_lock_map); return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 92e771d7b44b..2bc4e135ff23 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -93,6 +93,8 @@ int rcu_read_lock_bh_held(void) { if (!debug_lockdep_rcu_enabled()) return 1; + if (rcu_is_cpu_idle()) + return 0; return in_softirq() || irqs_disabled(); } EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 3ab77bdc90c4..b4e0b4981768 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -157,6 +157,7 @@ int rcu_is_cpu_idle(void) { return !rcu_dynticks_nesting; } +EXPORT_SYMBOL(rcu_is_cpu_idle); #endif /* #ifdef CONFIG_PROVE_RCU */ diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 8afb2e89745b..489b62a67d35 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -567,6 +567,7 @@ int rcu_is_cpu_idle(void) preempt_enable(); return ret; } +EXPORT_SYMBOL(rcu_is_cpu_idle); #endif /* #ifdef CONFIG_PROVE_RCU */ -- cgit From 00f49e5729af602deb559b0cf293a00b625e8636 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 7 Oct 2011 18:22:02 +0200 Subject: rcu: Warn when rcu_read_lock() is used in extended quiescent state We are currently able to detect uses of rcu_dereference_check() inside extended quiescent states (such as the RCU-free window in idle). But rcu_read_lock() and friends can be used without rcu_dereference(), so that the earlier commit checking for use of rcu_dereference() and friends while in RCU idle mode miss some error conditions. This commit therefore adds extended quiescent state checking to rcu_read_lock() and friends. Uses of RCU from within RCU-idle mode are totally ignored by RCU, hence the importance of these checks. Signed-off-by: Frederic Weisbecker Cc: Paul E. McKenney Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Lai Jiangshan Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 52 ++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 42 insertions(+), 10 deletions(-) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index bf91fcfe181c..d201c155f70c 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -237,21 +237,53 @@ static inline int rcu_is_cpu_idle(void) } #endif /* else !CONFIG_PROVE_RCU */ +static inline void rcu_lock_acquire(struct lockdep_map *map) +{ + WARN_ON_ONCE(rcu_is_cpu_idle()); + lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_); +} + +static inline void rcu_lock_release(struct lockdep_map *map) +{ + WARN_ON_ONCE(rcu_is_cpu_idle()); + lock_release(map, 1, _THIS_IP_); +} + extern struct lockdep_map rcu_lock_map; -# define rcu_read_acquire() \ - lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) -# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) + +static inline void rcu_read_acquire(void) +{ + rcu_lock_acquire(&rcu_lock_map); +} + +static inline void rcu_read_release(void) +{ + rcu_lock_release(&rcu_lock_map); +} extern struct lockdep_map rcu_bh_lock_map; -# define rcu_read_acquire_bh() \ - lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) -# define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) + +static inline void rcu_read_acquire_bh(void) +{ + rcu_lock_acquire(&rcu_bh_lock_map); +} + +static inline void rcu_read_release_bh(void) +{ + rcu_lock_release(&rcu_bh_lock_map); +} extern struct lockdep_map rcu_sched_lock_map; -# define rcu_read_acquire_sched() \ - lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) -# define rcu_read_release_sched() \ - lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) + +static inline void rcu_read_acquire_sched(void) +{ + rcu_lock_acquire(&rcu_sched_lock_map); +} + +static inline void rcu_read_release_sched(void) +{ + rcu_lock_release(&rcu_sched_lock_map); +} extern int debug_lockdep_rcu_enabled(void); -- cgit From d8ab29f8be918b34a1ccd174569a53f0eb04b0a5 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 7 Oct 2011 18:22:03 +0200 Subject: rcu: Remove one layer of abstraction from PROVE_RCU checking Simplify things a bit by substituting the definitions of the single-line rcu_read_acquire(), rcu_read_release(), rcu_read_acquire_bh(), rcu_read_release_bh(), rcu_read_acquire_sched(), and rcu_read_release_sched() functions at their call points. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 53 ++++++++---------------------------------------- 1 file changed, 8 insertions(+), 45 deletions(-) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index d201c155f70c..5dd6fd8b3203 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -250,41 +250,8 @@ static inline void rcu_lock_release(struct lockdep_map *map) } extern struct lockdep_map rcu_lock_map; - -static inline void rcu_read_acquire(void) -{ - rcu_lock_acquire(&rcu_lock_map); -} - -static inline void rcu_read_release(void) -{ - rcu_lock_release(&rcu_lock_map); -} - extern struct lockdep_map rcu_bh_lock_map; - -static inline void rcu_read_acquire_bh(void) -{ - rcu_lock_acquire(&rcu_bh_lock_map); -} - -static inline void rcu_read_release_bh(void) -{ - rcu_lock_release(&rcu_bh_lock_map); -} - extern struct lockdep_map rcu_sched_lock_map; - -static inline void rcu_read_acquire_sched(void) -{ - rcu_lock_acquire(&rcu_sched_lock_map); -} - -static inline void rcu_read_release_sched(void) -{ - rcu_lock_release(&rcu_sched_lock_map); -} - extern int debug_lockdep_rcu_enabled(void); /** @@ -364,12 +331,8 @@ static inline int rcu_read_lock_sched_held(void) #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ -# define rcu_read_acquire() do { } while (0) -# define rcu_read_release() do { } while (0) -# define rcu_read_acquire_bh() do { } while (0) -# define rcu_read_release_bh() do { } while (0) -# define rcu_read_acquire_sched() do { } while (0) -# define rcu_read_release_sched() do { } while (0) +# define rcu_lock_acquire(a) do { } while (0) +# define rcu_lock_release(a) do { } while (0) static inline int rcu_read_lock_held(void) { @@ -690,7 +653,7 @@ static inline void rcu_read_lock(void) { __rcu_read_lock(); __acquire(RCU); - rcu_read_acquire(); + rcu_lock_acquire(&rcu_lock_map); } /* @@ -710,7 +673,7 @@ static inline void rcu_read_lock(void) */ static inline void rcu_read_unlock(void) { - rcu_read_release(); + rcu_lock_release(&rcu_lock_map); __release(RCU); __rcu_read_unlock(); } @@ -731,7 +694,7 @@ static inline void rcu_read_lock_bh(void) { local_bh_disable(); __acquire(RCU_BH); - rcu_read_acquire_bh(); + rcu_lock_acquire(&rcu_bh_lock_map); } /* @@ -741,7 +704,7 @@ static inline void rcu_read_lock_bh(void) */ static inline void rcu_read_unlock_bh(void) { - rcu_read_release_bh(); + rcu_lock_release(&rcu_bh_lock_map); __release(RCU_BH); local_bh_enable(); } @@ -758,7 +721,7 @@ static inline void rcu_read_lock_sched(void) { preempt_disable(); __acquire(RCU_SCHED); - rcu_read_acquire_sched(); + rcu_lock_acquire(&rcu_sched_lock_map); } /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ @@ -775,7 +738,7 @@ static inline notrace void rcu_read_lock_sched_notrace(void) */ static inline void rcu_read_unlock_sched(void) { - rcu_read_release_sched(); + rcu_lock_release(&rcu_sched_lock_map); __release(RCU_SCHED); preempt_enable(); } -- cgit From 3842a0832a1d6eb0b31421f8810a813135967512 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 28 Nov 2011 10:42:42 -0800 Subject: rcu: Document same-context read-side constraints The intent is that a given RCU read-side critical section be confined to a single context. For example, it is illegal to invoke rcu_read_lock() in an exception handler and then invoke rcu_read_unlock() from the context of the task that received the exception. Suggested-by: Peter Zijlstra Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 15 +++++++++++++++ include/linux/srcu.h | 5 +++++ 2 files changed, 20 insertions(+) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 5dd6fd8b3203..81c04f4348ec 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -265,6 +265,11 @@ extern int debug_lockdep_rcu_enabled(void); * * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot * and while lockdep is disabled. + * + * Note that rcu_read_lock() and the matching rcu_read_unlock() must + * occur in the same context, for example, it is illegal to invoke + * rcu_read_unlock() in process context if the matching rcu_read_lock() + * was invoked from within an irq handler. */ static inline int rcu_read_lock_held(void) { @@ -689,6 +694,11 @@ static inline void rcu_read_unlock(void) * critical sections in interrupt context can use just rcu_read_lock(), * though this should at least be commented to avoid confusing people * reading the code. + * + * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() + * must occur in the same context, for example, it is illegal to invoke + * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() + * was invoked from some other task. */ static inline void rcu_read_lock_bh(void) { @@ -716,6 +726,11 @@ static inline void rcu_read_unlock_bh(void) * are being done using call_rcu_sched() or synchronize_rcu_sched(). * Read-side critical sections can also be introduced by anything that * disables preemption, including local_irq_disable() and friends. + * + * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() + * must occur in the same context, for example, it is illegal to invoke + * rcu_read_unlock_sched() from process context if the matching + * rcu_read_lock_sched() was invoked from an NMI handler. */ static inline void rcu_read_lock_sched(void) { diff --git a/include/linux/srcu.h b/include/linux/srcu.h index 1eb520cd1680..e1b005918bbb 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -158,6 +158,11 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp) * one way to indirectly wait on an SRCU grace period is to acquire * a mutex that is held elsewhere while calling synchronize_srcu() or * synchronize_srcu_expedited(). + * + * Note that srcu_read_lock() and the matching srcu_read_unlock() must + * occur in the same context, for example, it is illegal to invoke + * srcu_read_unlock() in an irq handler if the matching srcu_read_lock() + * was invoked in process context. */ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp) { -- cgit