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 <will.deacon@xxxxxxx> > AuthorDate: Thu, 16 Jul 2015 16:10:06 +0100 > Committer: Ingo Molnar <mingo@xxxxxxxxxx> > 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 <will.deacon@xxxxxxx> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx> > Cc: Douglas Hatch <doug.hatch@xxxxxx> > Cc: H. Peter Anvin <hpa@xxxxxxxxx> > Cc: Jonathan Corbet <corbet@xxxxxxx> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Scott J Norton <scott.norton@xxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Waiman Long <waiman.long@xxxxxx> > Link: http://lkml.kernel.org/r/20150716151006.GH26390@xxxxxxx > Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> > --- > 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-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
|