linux/include
Will Deacon 0bce9c46bf mutex: Place lock in contended state after fastpath_lock failure
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>
2012-08-13 18:46:54 +02:00
..
acpi Merge branches 'delete-gts-bfs', 'misc', 'novell-bugzilla-757888-numa' and 'osc-pcie' into base 2012-08-03 00:31:23 -04:00
asm-generic mutex: Place lock in contended state after fastpath_lock failure 2012-08-13 18:46:54 +02:00
crypto
drm drm/exynos: add property for plane zpos 2012-07-27 11:13:54 +09:00
keys
linux Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2012-08-13 09:18:19 +03:00
math-emu
media [media] v4l2: add core support for the new VIDIOC_ENUM_FREQ_BANDS ioctl 2012-07-30 20:23:05 -03:00
memory
misc
mtd
net codel: refine one condition to avoid a nul rec_inv_sqrt 2012-08-10 16:52:54 -07:00
pcmcia
ras
rdma Merge branches 'cma', 'cxgb4', 'misc', 'mlx4-sriov', 'mlx-cleanups', 'ocrdma' and 'qib' into for-linus 2012-07-22 23:26:17 -07:00
rxrpc
scsi Merge branch 'master' [vanilla Linus master] into libata-dev.git/upstream 2012-07-25 15:58:48 -04:00
sound Sound fixes for 3.6-rc1 2012-08-01 10:42:26 -07:00
target target: Allow for target_submit_cmd() returning errors 2012-07-17 17:05:05 -07:00
trace Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-08-03 10:57:20 -07:00
video video: da8xx-fb: configure FIFO threshold to reduce underflow errors 2012-07-29 01:11:09 +00:00
xen xen PVonHVM: move shared_info to MMIO before kexec 2012-07-19 15:52:05 -04:00
Kbuild