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Btrfs: fix race between direct io and autodefrag

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The bug is from running xfstests 209 with autodefrag.

The race is as follows:
       t1                       t2(autodefrag)
   direct IO
     invalidate pagecache
     dio(old data)             add_inode_defrag
     invalidate pagecache
   endio

   direct IO
     invalidate pagecache
                                run_defrag
                                  readpage(old data)
                                  set page dirty (old data)
     dio(new data, rewrite)
     invalidate pagecache (*)
     endio

t2(autodefrag) will get old data into pagecache via readpage and set
pagecache dirty.  Meanwhile, invalidate pagecache(*) will fail due to
dirty flags in pages.  So the old data may be flushed into disk by
flush thread, which will lead to data loss.

And so does the case of user defragment progs.

The patch fixes this race by holding i_mutex when we readpage and set page dirty.

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Liu Bo 2012-03-29 09:57:44 -04:00 committed by Chris Mason
parent 15d1ff8111
commit ecb8bea87d
1 changed files with 5 additions and 1 deletions
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6
fs/btrfs/ioctl.c
View file

@ -1137,12 +1137,16 @@ int btrfs_defrag_file(struct inode *inode, struct file *file,
ra_index += max_cluster;
}
mutex_lock(&inode->i_mutex);
ret = cluster_pages_for_defrag(inode, pages, i, cluster);
if (ret < 0)
if (ret < 0) {
mutex_unlock(&inode->i_mutex);
goto out_ra;
}
defrag_count += ret;
balance_dirty_pages_ratelimited_nr(inode->i_mapping, ret);
mutex_unlock(&inode->i_mutex);
if (newer_than) {
if (newer_off == (u64)-1)