Messages in this thread Patch in this message | | | Date | Fri, 3 Feb 2012 10:32:14 +0100 | From | Heiko Carstens <> | Subject | Re: rcu warnings cause stack overflow |
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On Thu, Feb 02, 2012 at 11:11:16AM -0800, Paul E. McKenney wrote: > On Thu, Feb 02, 2012 at 03:52:20PM +0100, Frederic Weisbecker wrote: > > On Thu, Feb 02, 2012 at 01:27:42PM +0100, Heiko Carstens wrote: > > > On Wed, Feb 01, 2012 at 04:14:48PM +0100, Frederic Weisbecker wrote: > > > > > Removing the WARN_ON_ONCE will fix this and, if lockdep is turned on, still > > > > > will find illegal uses. But it won't work for lockdep off configs... > > > > > So we probably want something better than the patch below. > > > > > > > > Ah ok. Hmm, but why are you using an exception to implement WARN_ON() > > > > in s390? Is it to have a whole new stack for the warning path in order > > > > to avoid stack overflow from the place that called the WARN_ON() ? > > > > > > The reason was to reduce the code footprint of the WARN_ON() and also > > > be able to print the register contents at the time the warning happened. > > > > Ah ok, makes sense. > > So Frederic should push his anti-recursion patch, then?
Yes, please.
Tested-by: Heiko Carstens <heiko.carstens@de.ibm.com>
It still generates recursive warnings because the WARNON_ONCE is inlined and every different usage will generate an exception, but it didn't produce a stack overflow anymore. To avoid the recursive warning the patch below would help. Not sure if it's worth it...
Subject: [PATCH] rcu: move rcu_is_cpu_idle() check warning into C file
From: Heiko Carstens <heiko.carstens@de.ibm.com>
rcu_read_lock() and rcu_read_unlock() generate a warning if a cpu is in extended quiescant state. Since these functions are inlined this can cause a lot of warnings if in the processing of the WARN_ON_ONCE() there is another usage of e.g. rcu_read_lock(). To make sure we only get one warning (and avoid possible stack overflows) uninline the check.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> --- include/linux/rcupdate.h | 9 +++++++-- kernel/rcupdate.c | 6 ++++++ 2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 81c04f4..9fe7be5 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -230,22 +230,27 @@ static inline void destroy_rcu_head_on_stack(struct rcu_head *head) #ifdef CONFIG_PROVE_RCU extern int rcu_is_cpu_idle(void); +extern void rcu_warn_if_is_cpu_idle(void); #else /* !CONFIG_PROVE_RCU */ static inline int rcu_is_cpu_idle(void) { return 0; } + +static inline void rcu_warn_if_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()); + rcu_warn_if_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()); + rcu_warn_if_is_cpu_idle(); lock_release(map, 1, _THIS_IP_); } diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 2bc4e13..5deca18 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -141,6 +141,12 @@ int rcu_my_thread_group_empty(void) return thread_group_empty(current); } EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty); + +void rcu_warn_if_is_cpu_idle(void) +{ + WARN_ON_ONCE(rcu_is_cpu_idle()); +} +EXPORT_SYMBOL_GPL(rcu_warn_if_is_cpu_idle); #endif /* #ifdef CONFIG_PROVE_RCU */ #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
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