From 66e8c57da6bf6b847a48a5a6fda59512f733ed78 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Tue, 25 Aug 2015 20:45:18 +0200 Subject: rcu: Change _wait_rcu_gp() to work around GCC bug 67055 Code like this in inline functions confuses some recent versions of gcc: const int n = const-expr; whatever_t array[n]; For more details, see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67055#c13 This compiler bug results in the following failure after 114b7fd4b (rcu: Create rcu_sync infrastructure): In file included from include/linux/rcupdate.h:429:0, from include/linux/rcu_sync.h:5, from kernel/rcu/sync.c:1: include/linux/rcutiny.h: In function 'rcu_barrier_sched': include/linux/rcutiny.h:55:20: internal compiler error: Segmentation fault static inline void rcu_barrier_sched(void) This commit therefore eliminates the constant local variable in favor of direct use of the expression. Reported-and-tested-by: Mark Salter Reported-by: Guenter Roeck Signed-off-by: Oleg Nesterov Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index ff476515f716..581abf848566 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -230,12 +230,11 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array, struct rcu_synchronize *rs_array); #define _wait_rcu_gp(checktiny, ...) \ -do { \ - call_rcu_func_t __crcu_array[] = { __VA_ARGS__ }; \ - const int __n = ARRAY_SIZE(__crcu_array); \ - struct rcu_synchronize __rs_array[__n]; \ - \ - __wait_rcu_gp(checktiny, __n, __crcu_array, __rs_array); \ +do { \ + call_rcu_func_t __crcu_array[] = { __VA_ARGS__ }; \ + struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)]; \ + __wait_rcu_gp(checktiny, ARRAY_SIZE(__crcu_array), \ + __crcu_array, __rs_array); \ } while (0) #define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__) -- cgit v1.2.2 From b6a4ae766e3133a4db73fabc81e522d1601cb623 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Wed, 29 Jul 2015 13:29:38 +0800 Subject: rcu: Use rcu_callback_t in call_rcu*() and friends As we now have rcu_callback_t typedefs as the type of rcu callbacks, we should use it in call_rcu*() and friends as the type of parameters. This could save us a few lines of code and make it clear which function requires an rcu callbacks rather than other callbacks as its argument. Besides, this can also help cscope to generate a better database for code reading. Signed-off-by: Boqun Feng Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 581abf848566..d63bb77dab35 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -160,7 +160,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename, * more than one CPU). */ void call_rcu(struct rcu_head *head, - void (*func)(struct rcu_head *head)); + rcu_callback_t func); #else /* #ifdef CONFIG_PREEMPT_RCU */ @@ -191,7 +191,7 @@ void call_rcu(struct rcu_head *head, * memory ordering guarantees. */ void call_rcu_bh(struct rcu_head *head, - void (*func)(struct rcu_head *head)); + rcu_callback_t func); /** * call_rcu_sched() - Queue an RCU for invocation after sched grace period. @@ -213,7 +213,7 @@ void call_rcu_bh(struct rcu_head *head, * memory ordering guarantees. */ void call_rcu_sched(struct rcu_head *head, - void (*func)(struct rcu_head *rcu)); + rcu_callback_t func); void synchronize_sched(void); @@ -274,7 +274,7 @@ do { \ * See the description of call_rcu() for more detailed information on * memory ordering guarantees. */ -void call_rcu_tasks(struct rcu_head *head, void (*func)(struct rcu_head *head)); +void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); void synchronize_rcu_tasks(void); void rcu_barrier_tasks(void); @@ -1065,7 +1065,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) #define __kfree_rcu(head, offset) \ do { \ BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ - kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \ + kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \ } while (0) /** -- cgit v1.2.2 From bb73c52bad3666997ed2ec83c0c80c3f8ef55008 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Thu, 30 Jul 2015 16:55:38 -0700 Subject: rcu: Don't disable preemption for Tiny and Tree RCU readers Because preempt_disable() maps to barrier() for non-debug builds, it forces the compiler to spill and reload registers. Because Tree RCU and Tiny RCU now only appear in CONFIG_PREEMPT=n builds, these barrier() instances generate needless extra code for each instance of rcu_read_lock() and rcu_read_unlock(). This extra code slows down Tree RCU and bloats Tiny RCU. This commit therefore removes the preempt_disable() and preempt_enable() from the non-preemptible implementations of __rcu_read_lock() and __rcu_read_unlock(), respectively. However, for debug purposes, preempt_disable() and preempt_enable() are still invoked if CONFIG_PREEMPT_COUNT=y, because this allows detection of sleeping inside atomic sections in non-preemptible kernels. However, Tiny and Tree RCU operates by coalescing all RCU read-side critical sections on a given CPU that lie between successive quiescent states. It is therefore necessary to compensate for removing barriers from __rcu_read_lock() and __rcu_read_unlock() by adding them to a couple of the RCU functions invoked during quiescent states, namely to rcu_all_qs() and rcu_note_context_switch(). However, note that the latter is more paranoia than necessity, at least until link-time optimizations become more aggressive. This is based on an earlier patch by Paul E. McKenney, fixing a bug encountered in kernels built with CONFIG_PREEMPT=n and CONFIG_PREEMPT_COUNT=y. Signed-off-by: Boqun Feng Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index d63bb77dab35..6c3ceceb6148 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -297,12 +297,14 @@ void synchronize_rcu(void); static inline void __rcu_read_lock(void) { - preempt_disable(); + if (IS_ENABLED(CONFIG_PREEMPT_COUNT)) + preempt_disable(); } static inline void __rcu_read_unlock(void) { - preempt_enable(); + if (IS_ENABLED(CONFIG_PREEMPT_COUNT)) + preempt_enable(); } static inline void synchronize_rcu(void) -- cgit v1.2.2 From c3ac7cf1847a4e68c909984f60d36adef2088e35 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 10 Sep 2015 16:29:02 -0700 Subject: rcu: Add rcu_pointer_handoff() This commit adds an rcu_pointer_handoff() that is intended to mark situations where a structure's protection transitions from RCU to some other mechanism (locking, reference counting, whatever). These markings should allow external tools to more easily spot bugs involving leaking pointers out of RCU read-side critical sections. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 6c3ceceb6148..587eb057e2fa 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -812,6 +812,28 @@ static inline void rcu_preempt_sleep_check(void) */ #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) +/** + * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism + * @p: The pointer to hand off + * + * This is simply an identity function, but it documents where a pointer + * is handed off from RCU to some other synchronization mechanism, for + * example, reference counting or locking. In C11, it would map to + * kill_dependency(). It could be used as follows: + * + * rcu_read_lock(); + * p = rcu_dereference(gp); + * long_lived = is_long_lived(p); + * if (long_lived) { + * if (!atomic_inc_not_zero(p->refcnt)) + * long_lived = false; + * else + * p = rcu_pointer_handoff(p); + * } + * rcu_read_unlock(); + */ +#define rcu_pointer_handoff(p) (p) + /** * rcu_read_lock() - mark the beginning of an RCU read-side critical section * -- cgit v1.2.2 From e62e3f620ba8d437f4998441fc11cf3dc9d466d1 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 14 Sep 2015 12:23:01 -0700 Subject: rcu: Remove deprecated rcu_lockdep_assert() The old rcu_lockdep_assert() was retained to ease handling of incoming patches, but any use will result in deprecated warnings. However, its replacement, RCU_LOCKDEP_WARN(), is now upstream. It is therefore time to remove rcu_lockdep_assert(), which this commit does. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- include/linux/rcupdate.h | 21 --------------------- 1 file changed, 21 deletions(-) (limited to 'include/linux/rcupdate.h') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 587eb057e2fa..a0189ba67fde 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -537,28 +537,8 @@ static inline int rcu_read_lock_sched_held(void) #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ -/* Deprecate rcu_lockdep_assert(): Use RCU_LOCKDEP_WARN() instead. */ -static inline void __attribute((deprecated)) deprecate_rcu_lockdep_assert(void) -{ -} - #ifdef CONFIG_PROVE_RCU -/** - * rcu_lockdep_assert - emit lockdep splat if specified condition not met - * @c: condition to check - * @s: informative message - */ -#define rcu_lockdep_assert(c, s) \ - do { \ - static bool __section(.data.unlikely) __warned; \ - deprecate_rcu_lockdep_assert(); \ - if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ - __warned = true; \ - lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ - } \ - } while (0) - /** * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met * @c: condition to check @@ -596,7 +576,6 @@ static inline void rcu_preempt_sleep_check(void) #else /* #ifdef CONFIG_PROVE_RCU */ -#define rcu_lockdep_assert(c, s) deprecate_rcu_lockdep_assert() #define RCU_LOCKDEP_WARN(c, s) do { } while (0) #define rcu_sleep_check() do { } while (0) -- cgit v1.2.2