From: "Aneesh Kumar K.V" Subject: [PATCH] ext4: Add WARN_ON on unmapped dirty buffer_heads in writepage Date: Thu, 28 May 2009 13:57:44 +0530 Message-ID: <1243499264-29629-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> Cc: linux-ext4@vger.kernel.org, "Aneesh Kumar K.V" To: cmm@us.ibm.com, tytso@mit.edu, sandeen@redhat.com, jack@suse.cz Return-path: Received: from e28smtp07.in.ibm.com ([59.145.155.7]:50348 "EHLO e28smtp07.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754103AbZE1I1s (ORCPT ); Thu, 28 May 2009 04:27:48 -0400 Received: from d28relay04.in.ibm.com (d28relay04.in.ibm.com [9.184.220.61]) by e28smtp07.in.ibm.com (8.13.1/8.13.1) with ESMTP id n4S8RlHa030690 for ; Thu, 28 May 2009 13:57:47 +0530 Received: from d28av05.in.ibm.com (d28av05.in.ibm.com [9.184.220.67]) by d28relay04.in.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n4S8RlVU1081510 for ; Thu, 28 May 2009 13:57:47 +0530 Received: from d28av05.in.ibm.com (loopback [127.0.0.1]) by d28av05.in.ibm.com (8.13.1/8.13.3) with ESMTP id n4S8Rkam008695 for ; Thu, 28 May 2009 18:27:47 +1000 Sender: linux-ext4-owner@vger.kernel.org List-ID: Now we have block_lock_hole_extend clearing the dirty flag of buffer_heads outside i_size we should not find buffer_heads which are unmapped and dirty in writepage. If we find do a WARN_ON. We can still continue because block_write_full page look at the mapped flag only. Following sequence of events would result in the above condition. 1) truncate(f, 1024) 2) mmap(f, 0, 4096) 3) a[0] = 'a' 4) truncate(f, 4096) 5) writepage(...) After step 3 we would have unmapped buffer_heads outside i_size. After step 4 we would have unmapped buffer_heads within i_size. Now that truncate is calling block_lock_hole_extend which in turn is clearing the dirty flag, we can safely assume that we won't find unmapped dirty buffer_heads in write page. If we did find one we should find out why. Signed-off-by: Aneesh Kumar K.V --- fs/ext4/inode.c | 13 +++++++++++++ 1 files changed, 13 insertions(+), 0 deletions(-) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index f6f2202..ca26bdd 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2509,6 +2509,11 @@ static int __ext4_journalled_writepage(struct page *page, return ret; } +static int ext4_bh_unmapped_and_dirty(handle_t *handle, struct buffer_head *bh) +{ + return (!buffer_mapped(bh)) && buffer_dirty(bh); +} + /* * Note that we don't need to start a transaction unless we're journaling data * because we should have holes filled from ext4_page_mkwrite(). We even don't @@ -2622,6 +2627,14 @@ static int ext4_writepage(struct page *page, /* now mark the buffer_heads as dirty and uptodate */ block_commit_write(page, 0, len); } + /* + * There should not be any unmapped and dirty + * buffer_heads at this point. Look at block_lock_hole_extend + * for more info. If we find one print more info + */ + WARN(walk_page_buffers(NULL, page_bufs, 0, len, NULL, + ext4_bh_unmapped_and_dirty), + "Unmapped dirty buffer_heads found in %s\n", __func__); if (PageChecked(page) && ext4_should_journal_data(inode)) { /* -- 1.6.3.1.145.gb74d77