From ca5ecddfa8fcbd948c95530e7e817cee9fb43a3d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 28 Apr 2010 14:39:09 -0700 Subject: rcu: define __rcu address space modifier for sparse This commit provides definitions for the __rcu annotation defined earlier. This annotation permits sparse to check for correct use of RCU-protected pointers. If a pointer that is annotated with __rcu is accessed directly (as opposed to via rcu_dereference(), rcu_assign_pointer(), or one of their variants), sparse can be made to complain. To enable such complaints, use the new default-disabled CONFIG_SPARSE_RCU_POINTER kernel configuration option. Please note that these sparse complaints are intended to be a debugging aid, -not- a code-style-enforcement mechanism. There are special rcu_dereference_protected() and rcu_access_pointer() accessors for use when RCU read-side protection is not required, for example, when no other CPU has access to the data structure in question or while the current CPU hold the update-side lock. This patch also updates a number of docbook comments that were showing their age. Signed-off-by: Arnd Bergmann Signed-off-by: Paul E. McKenney Cc: Christopher Li Reviewed-by: Josh Triplett --- kernel/rcupdate.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'kernel/rcupdate.c') diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 4d169835fb36..6c79e851521c 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -73,12 +73,14 @@ int debug_lockdep_rcu_enabled(void) EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); /** - * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section? + * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? * * Check for bottom half being disabled, which covers both the * CONFIG_PROVE_RCU and not cases. Note that if someone uses * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) - * will show the situation. + * will show the situation. This is useful for debug checks in functions + * that require that they be called within an RCU read-side critical + * section. * * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. */ -- cgit v1.2.2 From 773e3f93577ffb493fb7c39b1a6ecf39b5748e87 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 5 Oct 2010 14:03:02 -0700 Subject: rcu: move check from rcu_dereference_bh to rcu_read_lock_bh_held As suggested by Linus, push the irqs_disabled() down to the rcu_read_lock_bh_held() level so that all callers get the benefit of the correct check. Signed-off-by: Paul E. McKenney --- kernel/rcupdate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/rcupdate.c') diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 4d169835fb36..0af1dc70fece 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -86,7 +86,7 @@ int rcu_read_lock_bh_held(void) { if (!debug_lockdep_rcu_enabled()) return 1; - return in_softirq(); + return in_softirq() || irqs_disabled(); } EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); -- cgit v1.2.2 From fe8e64071a4ff5925ced4f33cb32ba090a04649c Mon Sep 17 00:00:00 2001 From: Amerigo Wang Date: Sun, 30 Jan 2011 18:23:08 +0800 Subject: rcupdate: remove dead code DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT, so #ifndef CONFIG_PREEMPT is totally useless in kernel/rcupdate.c. Signed-off-by: WANG Cong Cc: Paul E. McKenney Signed-off-by: Paul E. McKenney --- kernel/rcupdate.c | 5 ----- 1 file changed, 5 deletions(-) (limited to 'kernel/rcupdate.c') diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index a23a57a976d1..afd21d17c081 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -215,10 +215,6 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) * 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); @@ -229,7 +225,6 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) rcu_barrier_bh(); debug_object_free(head, &rcuhead_debug_descr); return 1; -#endif default: return 0; } -- cgit v1.2.2 From e611eecd6f9f91d74beda8cfbb3b5e02abdeb5a1 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 30 Jan 2011 23:56:46 -0800 Subject: rcu: add comment saying why DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT. The build will break if you change the Kconfig to allow DEBUG_OBJECTS_RCU_HEAD and !PREEMPT, so document the reasoning near where the breakage would occur. Signed-off-by: Paul E. McKenney --- kernel/rcupdate.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'kernel/rcupdate.c') diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index afd21d17c081..f3240e987928 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -214,6 +214,11 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) * 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. + * Note that the machinery to reliably determine whether + * or not we are in an RCU read-side critical section + * exists only in the preemptible RCU implementations + * (TINY_PREEMPT_RCU and TREE_PREEMPT_RCU), which is why + * DEBUG_OBJECTS_RCU_HEAD is disallowed if !PREEMPT. */ if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { -- cgit v1.2.2 From fc2ecf7ec76c5ee150b83dcefc863fa03fd365fb Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Wed, 23 Feb 2011 09:42:14 -0800 Subject: rcu: Enable DEBUG_OBJECTS_RCU_HEAD from !PREEMPT The prohibition of DEBUG_OBJECTS_RCU_HEAD from !PREEMPT was due to the fixup actions. So just produce a warning from !PREEMPT. Signed-off-by: Mathieu Desnoyers Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcupdate.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-) (limited to 'kernel/rcupdate.c') diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index f3240e987928..b54d6d18258c 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -142,7 +142,14 @@ static int rcuhead_fixup_init(void *addr, enum debug_obj_state state) * 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. + * In !PREEMPT configurations, there is no way to tell if we are + * in a RCU read-side critical section or not, so we never + * attempt any fixup and just print a warning. */ +#ifndef CONFIG_PREEMPT + WARN_ON(1); + return 0; +#endif if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { WARN_ON(1); @@ -184,7 +191,14 @@ static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) * 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. + * In !PREEMPT configurations, there is no way to tell if we are + * in a RCU read-side critical section or not, so we never + * attempt any fixup and just print a warning. */ +#ifndef CONFIG_PREEMPT + WARN_ON(1); + return 0; +#endif if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { WARN_ON(1); @@ -214,12 +228,14 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) * 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. - * Note that the machinery to reliably determine whether - * or not we are in an RCU read-side critical section - * exists only in the preemptible RCU implementations - * (TINY_PREEMPT_RCU and TREE_PREEMPT_RCU), which is why - * DEBUG_OBJECTS_RCU_HEAD is disallowed if !PREEMPT. + * In !PREEMPT configurations, there is no way to tell if we are + * in a RCU read-side critical section or not, so we never + * attempt any fixup and just print a warning. */ +#ifndef CONFIG_PREEMPT + WARN_ON(1); + return 0; +#endif if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { WARN_ON(1); -- cgit v1.2.2 From 108aae22339f445c134aeb48eca25df1014ab08d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 23 Feb 2011 09:56:00 -0800 Subject: rcu: Use WARN_ON_ONCE for DEBUG_OBJECTS_RCU_HEAD warnings Avoid additional multiple-warning confusion in memory-corruption scenarios. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcupdate.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'kernel/rcupdate.c') diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index b54d6d18258c..7784bd216b6a 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -147,12 +147,12 @@ static int rcuhead_fixup_init(void *addr, enum debug_obj_state state) * attempt any fixup and just print a warning. */ #ifndef CONFIG_PREEMPT - WARN_ON(1); + WARN_ON_ONCE(1); return 0; #endif if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { - WARN_ON(1); + WARN_ON_ONCE(1); return 0; } rcu_barrier(); @@ -196,12 +196,12 @@ static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) * attempt any fixup and just print a warning. */ #ifndef CONFIG_PREEMPT - WARN_ON(1); + WARN_ON_ONCE(1); return 0; #endif if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { - WARN_ON(1); + WARN_ON_ONCE(1); return 0; } rcu_barrier(); @@ -233,12 +233,12 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) * attempt any fixup and just print a warning. */ #ifndef CONFIG_PREEMPT - WARN_ON(1); + WARN_ON_ONCE(1); return 0; #endif if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { - WARN_ON(1); + WARN_ON_ONCE(1); return 0; } rcu_barrier(); -- cgit v1.2.2