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authorWill Deacon <will.deacon@arm.com>2018-02-13 13:30:19 +0000
committerIngo Molnar <mingo@kernel.org>2018-02-13 14:55:53 +0100
commit61e02392d3c7ecac1f91c0a90a8043d67e081846 (patch)
tree643df7dcf736a212690237f1b49ef108a2f096e6 /include
parent11dc13224c975efcec96647a4768a6f1bb7a19a8 (diff)
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locking/atomic/bitops: Document and clarify ordering semantics for failed test_and_{}_bit()
A test_and_{}_bit() operation fails if the value of the bit is such that the modification does not take place. For example, if test_and_set_bit() returns 1. In these cases, follow the behaviour of cmpxchg and allow the operation to be unordered. This also applies to test_and_set_bit_lock() if the lock is found to be be taken already. Signed-off-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1518528619-20049-1-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include')
-rw-r--r--include/asm-generic/bitops/lock.h3
1 files changed, 2 insertions, 1 deletions
diff --git a/include/asm-generic/bitops/lock.h b/include/asm-generic/bitops/lock.h
index bc397573c43a..67ab280ad134 100644
--- a/include/asm-generic/bitops/lock.h
+++ b/include/asm-generic/bitops/lock.h
@@ -7,7 +7,8 @@
* @nr: Bit to set
* @addr: Address to count from
*
- * This operation is atomic and provides acquire barrier semantics.
+ * This operation is atomic and provides acquire barrier semantics if
+ * the returned value is 0.
* It can be used to implement bit locks.
*/
#define test_and_set_bit_lock(nr, addr) test_and_set_bit(nr, addr)