Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967733AbWK3AfR (ORCPT ); Wed, 29 Nov 2006 19:35:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S967735AbWK3AfR (ORCPT ); Wed, 29 Nov 2006 19:35:17 -0500 Received: from host-233-54.several.ru ([213.234.233.54]:13535 "EHLO mail.screens.ru") by vger.kernel.org with ESMTP id S967733AbWK3AfP (ORCPT ); Wed, 29 Nov 2006 19:35:15 -0500 Date: Thu, 30 Nov 2006 03:35:06 +0300 From: Oleg Nesterov To: Andrew Morton Cc: David Howells , Alan Stern , "Paul E. McKenney" , linux-kernel@vger.kernel.org Subject: [PATCH] doc: atomic_add_unless() doesn't imply mb() on failure Message-ID: <20061130003506.GA1248@oleg> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1610 Lines: 38 Most implementations of atomic_add_unless() can fail (return 0) after the first atomic_read() (before cmpxchg). In that case we have a compiler barrier only. Signed-off-by: Oleg Nesterov Documentation/atomic_ops.txt | 3 ++- Documentation/memory-barriers.txt | 2 +- 2 files changed, 3 insertions(+), 2 deletions(-) --- 19-rc6/Documentation/memory-barriers.txt~doc 2006-11-27 21:20:20.000000000 +0300 +++ 19-rc6/Documentation/memory-barriers.txt 2006-11-30 03:32:06.000000000 +0300 @@ -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(); --- 19-rc6/Documentation/atomic_ops.txt~doc 2006-07-29 05:05:33.000000000 +0400 +++ 19-rc6/Documentation/atomic_ops.txt 2006-11-30 03:22:58.000000000 +0300 @@ -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) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/