f75d48644c
__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>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20160309114054.GJ6356@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
46 lines
1.2 KiB
C
46 lines
1.2 KiB
C
#ifndef _ASM_GENERIC_BITOPS_LOCK_H_
|
|
#define _ASM_GENERIC_BITOPS_LOCK_H_
|
|
|
|
/**
|
|
* test_and_set_bit_lock - Set a bit and return its old value, for lock
|
|
* @nr: Bit to set
|
|
* @addr: Address to count from
|
|
*
|
|
* This operation is atomic and provides acquire barrier semantics.
|
|
* It can be used to implement bit locks.
|
|
*/
|
|
#define test_and_set_bit_lock(nr, addr) test_and_set_bit(nr, addr)
|
|
|
|
/**
|
|
* clear_bit_unlock - Clear a bit in memory, for unlock
|
|
* @nr: the bit to set
|
|
* @addr: the address to start counting from
|
|
*
|
|
* This operation is atomic and provides release barrier semantics.
|
|
*/
|
|
#define clear_bit_unlock(nr, addr) \
|
|
do { \
|
|
smp_mb__before_atomic(); \
|
|
clear_bit(nr, addr); \
|
|
} while (0)
|
|
|
|
/**
|
|
* __clear_bit_unlock - Clear a bit in memory, for unlock
|
|
* @nr: the bit to set
|
|
* @addr: the address to start counting from
|
|
*
|
|
* A weaker form of clear_bit_unlock() as used by __bit_lock_unlock(). If all
|
|
* the bits in the word are protected by this lock some archs can use weaker
|
|
* ops to safely unlock.
|
|
*
|
|
* See for example x86's implementation.
|
|
*/
|
|
#define __clear_bit_unlock(nr, addr) \
|
|
do { \
|
|
smp_mb__before_atomic(); \
|
|
clear_bit(nr, addr); \
|
|
} while (0)
|
|
|
|
#endif /* _ASM_GENERIC_BITOPS_LOCK_H_ */
|
|
|