Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750888AbWC1D7J (ORCPT ); Mon, 27 Mar 2006 22:59:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750972AbWC1D7J (ORCPT ); Mon, 27 Mar 2006 22:59:09 -0500 Received: from omx1-ext.sgi.com ([192.48.179.11]:34183 "EHLO omx1.americas.sgi.com") by vger.kernel.org with ESMTP id S1750839AbWC1D7H (ORCPT ); Mon, 27 Mar 2006 22:59:07 -0500 Date: Mon, 27 Mar 2006 19:59:02 -0800 (PST) From: Christoph Lameter To: akpm@osdl.org cc: nickpiggin@yahoo.com.au, Zoltan.Menyhart@free.fr, linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org Subject: Fix unlock_buffer() to work the same way as bit_unlock() Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1764 Lines: 48 Currently unlock_buffer() contains a smb_mb__after_clear_bit() which is weird because bit_spin_unlock() uses smb_mb__before_clear_bit(): >From include/linux/bit_spinlock.h: static inline void bit_spin_unlock(int bitnum, unsigned long *addr) { smp_mb__before_clear_bit(); clear_bit(bitnum, addr); preempt_enable(); __release(bitlock); } For most architectures there is no difference because both smp_mb__after_clear_bit() and smp_mb__before_clear_bit() are both memory barriers and clear_buffer_locked() is an atomic operation. However, they differ under IA64. Note that this potential race has never been seen under IA64. It was discovered by inspection by Zoltan Menyhart . Regardless if this is a true race or not, I think the unlock sequence needs to be the same for bit locks and unlock_buffer(). Maybe unlock_buffer and lock_buffer better use bit spinlock operations? Change unlock_buffer() to work the same way as bit_spin_unlock. Signed-off-by: Christoph Lameter Index: linux-2.6/fs/buffer.c =================================================================== --- linux-2.6.orig/fs/buffer.c 2006-03-27 14:09:54.000000000 -0800 +++ linux-2.6/fs/buffer.c 2006-03-27 19:40:32.000000000 -0800 @@ -78,8 +78,8 @@ EXPORT_SYMBOL(__lock_buffer); void fastcall unlock_buffer(struct buffer_head *bh) { + smp_mb__before_clear_bit(); clear_buffer_locked(bh); - smp_mb__after_clear_bit(); wake_up_bit(&bh->b_state, BH_Lock); } - 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/