android_kernel_oneplus_msm8998/include
Peter Zijlstra 2bfb843538 bitops: Do not default to __clear_bit() for __clear_bit_unlock()
commit f75d48644c56a31731d17fa693c8175328957e1d upstream.

__clear_bit_unlock() is a special little snowflake. While it carries the
non-atomic '__' prefix, it is specifically documented to pair with
test_and_set_bit() and therefore should be 'somewhat' atomic.

Therefore the generic implementation of __clear_bit_unlock() cannot use
the fully non-atomic __clear_bit() as a default.

If an arch is able to do better; is must provide an implementation of
__clear_bit_unlock() itself.

Specifically, this came up as a result of hackbench livelock'ing in
slab_lock() on ARC with SMP + SLUB + !LLSC.

The issue was incorrect pairing of atomic ops.

 slab_lock() -> bit_spin_lock() -> test_and_set_bit()
 slab_unlock() -> __bit_spin_unlock() -> __clear_bit()

The non serializing __clear_bit() was getting "lost"

 80543b8e:	ld_s       r2,[r13,0] <--- (A) Finds PG_locked is set
 80543b90:	or         r3,r2,1    <--- (B) other core unlocks right here
 80543b94:	st_s       r3,[r13,0] <--- (C) sets PG_locked (overwrites unlock)

Fixes ARC STAR 9000817404 (and probably more).

Reported-by: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Tested-by: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Helge Deller <deller@gmx.de>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Noam Camus <noamc@ezchip.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160309114054.GJ6356@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2016-04-12 09:09:00 -07:00
..
acpi Merge branch 'acpi-pci' 2015-11-07 01:30:10 +01:00
asm-generic bitops: Do not default to __clear_bit() for __clear_bit_unlock() 2016-04-12 09:09:00 -07:00
clocksource
crypto crypto: af_alg - Allow af_af_alg_release_parent to be called on nokey path 2016-02-17 12:31:03 -08:00
drm drm: add helper to check for wc memory support 2016-03-03 15:07:21 -08:00
dt-bindings ARM: DT updates for v4.4 2015-11-10 15:06:26 -08:00
keys
kvm KVM: arm/arm64: arch_timer: Preserve physical dist. active state on LR.active 2015-11-24 18:07:40 +01:00
linux tracing: Fix trace_printk() to print when not using bprintk() 2016-04-12 09:09:00 -07:00
math-emu
media
memory
misc
net cfg80211/wext: fix message ordering 2016-03-16 08:42:59 -07:00
pcmcia
ras
rdma IB/mad: Require CM send method for everything except ClassPortInfo 2015-12-08 12:19:11 -05:00
rxrpc
scsi Merge branch 'mkp-fixes' into fixes 2015-12-03 09:32:33 -08:00
soc ARM: SoC driver updates for v4.4 2015-11-10 15:00:03 -08:00
sound ALSA: rawmidi: Make snd_rawmidi_transmit() race-free 2016-02-17 12:30:58 -08:00
target target: Fix WRITE_SAME/DISCARD conversion to linux 512b sectors 2016-03-09 15:34:51 -08:00
trace Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/rzhang/linux 2015-11-11 09:03:01 -08:00
uapi uapi: update install list after nvme.h rename 2016-03-03 15:07:24 -08:00
video gpu: ipu-v3: drop unused dmfc field from client platform data 2015-11-24 11:30:15 +01:00
xen xen: Add RING_COPY_REQUEST() 2015-12-18 10:00:17 -05:00
Kbuild