Currently if DEBUG_MUTEXES is enabled, the mutex->owner field is only
cleared iff debug_locks is active. This exposes a race to other users of
the field where the mutex->owner may be still set to a stale value,
potentially upsetting mutex_spin_on_owner() among others.
References: https://bugs.freedesktop.org/show_bug.cgi?id=87955
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1420540175-30204-1-git-send-email-chris@chris-wilson.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>
debug_mutex_unlock() would bail when !debug_locks and forgets to
actually unlock.
Reported-by: "Michael L. Semon" <mlsemon35@gmail.com>
Reported-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Fixes: 6f008e72cd ("locking/mutex: Fix debug checks")
Tested-by: Dave Jones <davej@redhat.com>
Cc: Jason Low <jason.low2@hp.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140410141559.GE13658@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
OK, so commit:
1d8fe7dc80 ("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>
When mutex debugging is enabled and an imbalanced mutex_unlock()
is called, we get the following, slightly confusing warning:
[ 364.208284] DEBUG_LOCKS_WARN_ON(lock->owner != current)
But in that case the warning is due to an imbalanced mutex_unlock() call,
and the lock->owner is NULL - so the message is misleading.
So improve the message by testing for this case specifically:
DEBUG_LOCKS_WARN_ON(!lock->owner)
Signed-off-by: Liu, Chuansheng <chuansheng.liu@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1386136693.3650.48.camel@cliu38-desktop-build
[ Improved the changelog, changed the patch to use !lock->owner consistently. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Chris Wilson
Peter Zijlstra
Chuansheng Liu