From: "Aneesh Kumar K.V" Subject: Re: [PATCH] fix ext4_free_inode vs. ext4_claim_inode race Date: Thu, 5 Mar 2009 00:36:59 +0530 Message-ID: <20090304190659.GB17949@skywalker> References: <49AE05D1.9050607@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: ext4 development To: Eric Sandeen Return-path: Received: from e28smtp02.in.ibm.com ([59.145.155.2]:56965 "EHLO e28smtp02.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751849AbZCDTHK (ORCPT ); Wed, 4 Mar 2009 14:07:10 -0500 Received: from d28relay02.in.ibm.com (d28relay02.in.ibm.com [9.184.220.59]) by e28smtp02.in.ibm.com (8.13.1/8.13.1) with ESMTP id n24J76tB006863 for ; Thu, 5 Mar 2009 00:37:06 +0530 Received: from d28av01.in.ibm.com (d28av01.in.ibm.com [9.184.220.63]) by d28relay02.in.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n24J451i2396316 for ; Thu, 5 Mar 2009 00:34:05 +0530 Received: from d28av01.in.ibm.com (loopback [127.0.0.1]) by d28av01.in.ibm.com (8.13.1/8.13.3) with ESMTP id n24J75wl017906 for ; Thu, 5 Mar 2009 00:37:06 +0530 Content-Disposition: inline In-Reply-To: <49AE05D1.9050607@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Mar 03, 2009 at 10:38:41PM -0600, Eric Sandeen wrote: > I was seeing fsck errors on inode bitmaps after a 4 thread > dbench run on a 4 cpu machine: > > Inode bitmap differences: -50736 -(50752--50753) etc... > > I believe that this is because ext4_free_inode() uses atomic > bitops, and although ext4_new_inode() *used* to also use atomic > bitops for synchronization, commit > 393418676a7602e1d7d3f6e560159c65c8cbd50e changed this to use > the sb_bgl_lock, so that we could also synchronize against > read_inode_bitmap and initialization of uninit inode tables. > > However, that change left ext4_free_inode using atomic bitops, > which I think leaves no synchronization between setting & > unsetting bits in the inode table. > > The below patch fixes it for me, although I wonder if we're > getting at all heavy-handed with this spinlock... > > Signed-off-by: Eric Sandeen Reviewed-by: Aneesh Kumar K.V > --- > > Index: linux-2.6/fs/ext4/ialloc.c > =================================================================== > --- linux-2.6.orig/fs/ext4/ialloc.c > +++ linux-2.6/fs/ext4/ialloc.c > @@ -188,7 +188,7 @@ void ext4_free_inode(handle_t *handle, s > struct ext4_group_desc *gdp; > struct ext4_super_block *es; > struct ext4_sb_info *sbi; > - int fatal = 0, err, count; > + int fatal = 0, err, count, cleared; > ext4_group_t flex_group; > > if (atomic_read(&inode->i_count) > 1) { > @@ -248,8 +248,10 @@ void ext4_free_inode(handle_t *handle, s > goto error_return; > > /* Ok, now we can actually update the inode bitmaps.. */ > - if (!ext4_clear_bit_atomic(sb_bgl_lock(sbi, block_group), > - bit, bitmap_bh->b_data)) > + spin_lock(sb_bgl_lock(sbi, block_group)); > + cleared = ext4_clear_bit(bit, bitmap_bh->b_data); > + spin_unlock(sb_bgl_lock(sbi, block_group)); > + if (!cleared) > ext4_error(sb, "ext4_free_inode", > "bit already cleared for inode %lu", ino); > else { >