Messages in this thread Patch in this message | | | Date | Thu, 13 Mar 2014 00:28:18 -0700 | From | tip-bot for Peter Zijlstra <> | Subject | [tip:core/locking] locking/mutex: Fix debug checks |
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Commit-ID: 6f008e72cd111a119b5d8de8c5438d892aae99eb Gitweb: http://git.kernel.org/tip/6f008e72cd111a119b5d8de8c5438d892aae99eb Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Wed, 12 Mar 2014 13:24:42 +0100 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 12 Mar 2014 13:49:47 +0100
locking/mutex: Fix debug checks
OK, so commit:
1d8fe7dc8078 ("locking/mutexes: Unlock the mutex without the wait_lock")
generates this boot warning when CONFIG_DEBUG_MUTEXES=y:
WARNING: CPU: 0 PID: 139 at /usr/src/linux-2.6/kernel/locking/mutex-debug.c:82 debug_mutex_unlock+0x155/0x180() DEBUG_LOCKS_WARN_ON(lock->owner != current)
And that makes sense, because as soon as we release the lock a new owner can come in...
One would think that !__mutex_slowpath_needs_to_unlock() implementations suffer the same, but for DEBUG we fall back to mutex-null.h which has an unconditional 1 for that.
The mutex debug code requires the mutex to be unlocked after doing the debug checks, otherwise it can find inconsistent state.
Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: jason.low2@hp.com Link: http://lkml.kernel.org/r/20140312122442.GB27965@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/locking/mutex-debug.c | 6 ++++++ kernel/locking/mutex.c | 7 +++++++ 2 files changed, 13 insertions(+)
diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c index faf6f5b..e1191c9 100644 --- a/kernel/locking/mutex-debug.c +++ b/kernel/locking/mutex-debug.c @@ -83,6 +83,12 @@ void debug_mutex_unlock(struct mutex *lock) DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next); mutex_clear_owner(lock); + + /* + * __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug + * mutexes so that we can do it here after we've verified state. + */ + atomic_set(&lock->count, 1); } void debug_mutex_init(struct mutex *lock, const char *name, diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 02c61a9..14fe72c 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -34,6 +34,13 @@ #ifdef CONFIG_DEBUG_MUTEXES # include "mutex-debug.h" # include <asm-generic/mutex-null.h> +/* + * Must be 0 for the debug case so we do not do the unlock outside of the + * wait_lock region. debug_mutex_unlock() will do the actual unlock in this + * case. + */ +# undef __mutex_slowpath_needs_to_unlock +# define __mutex_slowpath_needs_to_unlock() 0 #else # include "mutex.h" # include <asm/mutex.h>
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