On Mon, 2015-08-03 at 09:59 -0700, tip-bot for Will Deacon wrote: > Commit-ID: ed2de9f74ecbbf3063d29b2334e7b455d7f35189 > Gitweb: http://git.kernel.org/tip/ed2de9f74ecbbf3063d29b2334e7b455d7f35189 > Author: Will Deacon <[email protected]> > AuthorDate: Thu, 16 Jul 2015 16:10:06 +0100 > Committer: Ingo Molnar <[email protected]> > CommitDate: Mon, 3 Aug 2015 10:57:09 +0200 > > locking/Documentation: Clarify failed cmpxchg() memory ordering semantics > > A failed cmpxchg does not provide any memory ordering guarantees, a > property that is used to optimise the cmpxchg implementations on Alpha, > PowerPC and arm64. > > This patch updates atomic_ops.txt and memory-barriers.txt to reflect > this. > > Signed-off-by: Will Deacon <[email protected]> > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: Davidlohr Bueso <[email protected]> > Cc: Douglas Hatch <[email protected]> > Cc: H. Peter Anvin <[email protected]> > Cc: Jonathan Corbet <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Paul E. McKenney <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Scott J Norton <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Waiman Long <[email protected]> > Link: http://lkml.kernel.org/r/[email protected] > Signed-off-by: Ingo Molnar <[email protected]> > --- > Documentation/atomic_ops.txt | 4 +++- > Documentation/memory-barriers.txt | 6 +++--- > 2 files changed, 6 insertions(+), 4 deletions(-) > > diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt > index dab6da3..b19fc34 100644 > --- a/Documentation/atomic_ops.txt > +++ b/Documentation/atomic_ops.txt > @@ -266,7 +266,9 @@ with the given old and new values. Like all atomic_xxx > operations, > atomic_cmpxchg will only satisfy its atomicity semantics as long as all > other accesses of *v are performed through atomic_xxx operations. > > -atomic_cmpxchg must provide explicit memory barriers around the operation. > +atomic_cmpxchg must provide explicit memory barriers around the operation, > +although if the comparison fails then no memory ordering guarantees are > +required.
Thanks, I also stumbled upon this with the wake-q stuff. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
