This is a note to let you know that I've just added the patch titled ext4: fix extent status tree race in writeback error recovery path to the 5.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ext4-fix-extent-status-tree-race-in-writeback-error-.patch and it can be found in the queue-5.18 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit dc4a02f5902dad0bd2ac7063ad9cc82a29f579f2 Author: Eric Whitney <enwlinux@xxxxxxxxx> Date: Wed Jun 15 12:05:30 2022 -0400 ext4: fix extent status tree race in writeback error recovery path [ Upstream commit 7f0d8e1d607c1a4fa9a27362a108921d82230874 ] A race can occur in the unlikely event ext4 is unable to allocate a physical cluster for a delayed allocation in a bigalloc file system during writeback. Failure to allocate a cluster forces error recovery that includes a call to mpage_release_unused_pages(). That function removes any corresponding delayed allocated blocks from the extent status tree. If a new delayed write is in progress on the same cluster simultaneously, resulting in the addition of an new extent containing one or more blocks in that cluster to the extent status tree, delayed block accounting can be thrown off if that delayed write then encounters a similar cluster allocation failure during future writeback. Write lock the i_data_sem in mpage_release_unused_pages() to fix this problem. Ext4's block/cluster accounting code for bigalloc relies on i_data_sem for mutual exclusion, as is found in the delayed write path, and the locking in mpage_release_unused_pages() is missing. Cc: stable@xxxxxxxxxx Reported-by: Ye Bin <yebin10@xxxxxxxxxx> Signed-off-by: Eric Whitney <enwlinux@xxxxxxxxx> Link: https://lore.kernel.org/r/20220615160530.1928801-1-enwlinux@xxxxxxxxx Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index beed9e32571c..826e2deb10f8 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -1559,7 +1559,14 @@ static void mpage_release_unused_pages(struct mpage_da_data *mpd, ext4_lblk_t start, last; start = index << (PAGE_SHIFT - inode->i_blkbits); last = end << (PAGE_SHIFT - inode->i_blkbits); + + /* + * avoid racing with extent status tree scans made by + * ext4_insert_delayed_block() + */ + down_write(&EXT4_I(inode)->i_data_sem); ext4_es_remove_extent(inode, start, last - start + 1); + up_write(&EXT4_I(inode)->i_data_sem); } pagevec_init(&pvec);