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Date: Thu, 23 Aug 2007 16:49:53 +1000 From: Nick Piggin <nickpiggin@...oo.com.au> To: Oleg Nesterov <oleg@...sign.ru> CC: Andrew Morton <akpm@...ux-foundation.org>, David Howells <dhowells@...hat.com>, "David S. Miller" <davem@...emloft.net>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH,RESEND] documentation: atomic_add_unless() doesn't imply mb() on failure Oleg Nesterov wrote: > (the explicit ack/nack from maintainers is wanted). > > A "typical" implementation of atomic_add_unless() can return 0 immediately > after the first atomic_read() (before doing cmpxchg). In that case it doesn't > provide any barrier semantics. See include/asm-ia64/atomic.h as an example. > > We should either change the implementation, or fix the docs. Did this end up getting merged? If not, it should, thanks. Acked-by: Nick Piggin <npiggin@...e.de> > > Signed-off-by: Oleg Nesterov <oleg@...sign.ru> > > Documentation/atomic_ops.txt | 3 ++- > Documentation/memory-barriers.txt | 2 +- > 2 files changed, 3 insertions(+), 2 deletions(-) > > diff -puN Documentation/atomic_ops.txt~doc-atomic_add_unless-doesnt-imply-mb-on-failure Documentation/atomic_ops.txt > --- a/Documentation/atomic_ops.txt~doc-atomic_add_unless-doesnt-imply-mb-on-failure > +++ a/Documentation/atomic_ops.txt > @@ -137,7 +137,8 @@ If the atomic value v is not equal to u, > returns non zero. If v is equal to u then it returns zero. This is done as > an atomic operation. > > -atomic_add_unless requires explicit memory barriers around the operation. > +atomic_add_unless requires explicit memory barriers around the operation > +unless it fails (returns 0). > > atomic_inc_not_zero, equivalent to atomic_add_unless(v, 1, 0) > > diff -puN Documentation/memory-barriers.txt~doc-atomic_add_unless-doesnt-imply-mb-on-failure Documentation/memory-barriers.txt > --- a/Documentation/memory-barriers.txt~doc-atomic_add_unless-doesnt-imply-mb-on-failure > +++ a/Documentation/memory-barriers.txt > @@ -1492,7 +1492,7 @@ about the state (old or new) implies an > atomic_dec_and_test(); > atomic_sub_and_test(); > atomic_add_negative(); > - atomic_add_unless(); > + atomic_add_unless(); /* when succeeds (returns 1) */ > test_and_set_bit(); > test_and_clear_bit(); > test_and_change_bit(); > _ > > -- SUSE Labs, Novell Inc. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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