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* mutex: Place lock in contended state after fastpath_lock failureWill Deacon2012-08-131-2/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | ARM recently moved to asm-generic/mutex-xchg.h for its mutex implementation after the previous implementation was found to be missing some crucial memory barriers. However, this has revealed some problems running hackbench on SMP platforms due to the way in which the MUTEX_SPIN_ON_OWNER code operates. The symptoms are that a bunch of hackbench tasks are left waiting on an unlocked mutex and therefore never get woken up to claim it. This boils down to the following sequence of events: Task A Task B Task C Lock value 0 1 1 lock() 0 2 lock() 0 3 spin(A) 0 4 unlock() 1 5 lock() 0 6 cmpxchg(1,0) 0 7 contended() -1 8 lock() 0 9 spin(C) 0 10 unlock() 1 11 cmpxchg(1,0) 0 12 unlock() 1 At this point, the lock is unlocked, but Task B is in an uninterruptible sleep with nobody to wake it up. This patch fixes the problem by ensuring we put the lock into the contended state if we fail to acquire it on the fastpath, ensuring that any blocked waiters are woken up when the mutex is released. Signed-off-by: Will Deacon <will.deacon@arm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Chris Mason <chris.mason@fusionio.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: <stable@vger.kernel.org> Reviewed-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/n/tip-6e9lrw2avczr0617fzl5vqb8@git.kernel.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* mutex: speed up generic mutex implementationsNick Piggin2008-10-231-8/+1
| | | | | | | | | | | | | | | | | - atomic operations which both modify the variable and return something imply full smp memory barriers before and after the memory operations involved (failing atomic_cmpxchg, atomic_add_unless, etc don't imply a barrier because they don't modify the target). See Documentation/atomic_ops.txt. So remove extra barriers and branches. - All architectures support atomic_cmpxchg. This has no relation to __HAVE_ARCH_CMPXCHG. We can just take the atomic_cmpxchg path unconditionally This reduces a simple single threaded fastpath lock+unlock test from 590 cycles to 203 cycles on a ppc970 system. Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* asm-generic: remove fastcallHarvey Harrison2008-02-081-3/+3
| | | | | | Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* fix file specification in commentsUwe Zeisberger2006-10-031-1/+1
| | | | | | | Many files include the filename at the beginning, serveral used a wrong one. Signed-off-by: Uwe Zeisberger <Uwe_Zeisberger@digi.com> Signed-off-by: Adrian Bunk <bunk@stusta.de>
* [PATCH] mutex: some cleanupsNicolas Pitre2006-03-311-16/+17
| | | | | | | | | | Turn some macros into inline functions and add proper type checking as well as being more readable. Also a minor comment adjustment. Signed-off-by: Nicolas Pitre <nico@cam.org> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
* [PATCH] mutex subsystem, add asm-generic/mutex-[dec|xchg|null].h implementationsIngo Molnar2006-01-091-0/+117
Add three (generic) mutex fastpath implementations. The mutex-xchg.h implementation is atomic_xchg() based, and should work fine on every architecture. The mutex-dec.h implementation is atomic_dec_return() based - this one too should work on every architecture, but might not perform the most optimally on architectures that have no atomic-dec/inc instructions. The mutex-null.h implementation forces all calls into the slowpath. This is used for mutex debugging, but it can also be used on platforms that do not want (or need) a fastpath at all. Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Arjan van de Ven <arjan@infradead.org>
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