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The current mutex implementation has an atomic lock word and a non-atomic owner field. This disparity leads to a number of issues with the current mutex code as it means that we can have a locked mutex without an explicit owner (because the owner field has not been set, or already cleared). This leads to a number of weird corner cases, esp. between the optimistic spinning and debug code. Where the optimistic spinning code needs the owner field updated inside the lock region, the debug code is more relaxed because the whole lock is serialized by the wait_lock. Also, the spinning code itself has a few corner cases where we need to deal with a held lock without an owner field. Furthermore, it becomes even more of a problem when trying to fix starvation cases in the current code. We end up stacking special case on special case. To solve this rework the basic mutex implementation to be a single atomic word that contains the owner and uses the low bits for extra state. This matches how PI futexes and rt_mutex already work. By having the owner an integral part of the lock state a lot of the problems dissapear and we get a better option to deal with starvation cases, direct owner handoff. Changing the basic mutex does however invalidate all the arch specific mutex code; this patch leaves that unused in-place, a later patch will remove that. Tested-by: Jason Low <jason.low2@hpe.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Will Deacon <will.deacon@arm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> 
Peter Zijlstra
authored and
 Ingo Molnar
commited |
3ca0ff571b | |
None of the code actually wants a thread_info, it all wants a
task_struct, and it's just converting back and forth between the two
("ti->task" to get the task_struct from the thread_info, and
"task_thread_info(task)" to go the other way).
No semantic change.
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linus Torvalds
commited |
6720a305df | |
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> 
Chris Wilson
authored and
Ingo Molnar
commited |
a63b03e2d2 | |
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:
Peter Zijlstra
authored and
Ingo Molnar
commited |
a227960fe0 | |
OK, so commit:
Peter Zijlstra
authored and
Ingo Molnar
commited |
6f008e72cd | |
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> 
Chuansheng Liu
authored and
Ingo Molnar
commited |
91f30a1702 | |
Suggested-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/n/tip-1ditvncg30dgbpvrz2bxfmke@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Peter Zijlstra
authored and
Ingo Molnar
commited |
01768b42dc |
Renamed from kernel/mutex-debug.c (Browse further)