Will Deacon e60b883144 mutex: Place lock in contended state after fastpath_lock failure ... commit 0bce9c46bf upstream. 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> 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2012-10-02 10:30:21 -07:00
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acpi	Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux	2012-05-05 10:06:06 -07:00
asm-generic	mutex: Place lock in contended state after fastpath_lock failure	2012-10-02 10:30:21 -07:00
crypto	crypto: user - Fix lookup of algorithms with IV generator	2012-03-29 19:52:47 +08:00
drm	drm/radeon: add some new SI pci ids	2012-08-26 15:00:41 -07:00
keys
linux	NFS: Fix the initialisation of the readdir 'cookieverf' array	2012-10-02 10:30:19 -07:00
math-emu
media	Merge branch 'v4l_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media	2012-05-14 11:23:37 -07:00
misc
mtd
net	af_netlink: force credentials passing [CVE-2012-3520]	2012-10-02 10:29:37 -07:00
pcmcia
rdma	Merge branches 'cma', 'cxgb3', 'cxgb4', 'ehca', 'iser', 'mad', 'nes', 'qib', 'srp' and 'srpt' into for-next	2012-03-19 09:50:33 -07:00
rxrpc
scsi	SCSI: libsas: fix taskfile corruption in sas_ata_qc_fill_rtf	2012-07-16 09:04:37 -07:00
sound	ALSA: hda - hide HDMI/ELD printks unless snd.debug=2	2012-04-10 14:53:55 +02:00
target	target: Add generation of LOGICAL BLOCK ADDRESS OUT OF RANGE	2012-08-09 08:31:26 -07:00
trace	tracing: Don't call page_to_pfn() if page is NULL	2012-10-02 10:30:08 -07:00
video	Merge branch 'platforms' of git://git.linaro.org/people/rmk/linux-arm	2012-03-27 18:17:02 -07:00
xen	xen/m2p: do not reuse kmap_op->dev_bus_addr	2012-10-02 10:30:06 -07:00
Kbuild