This is a note to let you know that I've just added the patch titled
ext4: fix warning in ext4_dio_write_end_io()
to the 6.6-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-warning-in-ext4_dio_write_end_io.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 8a562e59fd9305ab22dfd80196bea309087fd560
Author: Jan Kara <jack@xxxxxxx>
Date: Thu Nov 30 10:56:53 2023 +0100
ext4: fix warning in ext4_dio_write_end_io()
[ Upstream commit 619f75dae2cf117b1d07f27b046b9ffb071c4685 ]
The syzbot has reported that it can hit the warning in
ext4_dio_write_end_io() because i_size < i_disksize. Indeed the
reproducer creates a race between DIO IO completion and truncate
expanding the file and thus ext4_dio_write_end_io() sees an inconsistent
inode state where i_disksize is already updated but i_size is not
updated yet. Since we are careful when setting up DIO write and consider
it extending (and thus performing the IO synchronously with i_rwsem held
exclusively) whenever it goes past either of i_size or i_disksize, we
can use the same test during IO completion without risking entering
ext4_handle_inode_extension() without i_rwsem held. This way we make it
obvious both i_size and i_disksize are large enough when we report DIO
completion without relying on unreliable WARN_ON.
Reported-by: <syzbot+47479b71cdfc78f56d30@xxxxxxxxxxxxxxxxxxxxxxxxx>
Fixes: 91562895f803 ("ext4: properly sync file size update after O_SYNC direct IO")
Signed-off-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
Link: https://lore.kernel.org/r/20231130095653.22679-1-jack@xxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 0166bb9ca160b..6aa15dafc6778 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -349,9 +349,10 @@ static void ext4_inode_extension_cleanup(struct inode *inode, ssize_t count)
return;
}
/*
- * If i_disksize got extended due to writeback of delalloc blocks while
- * the DIO was running we could fail to cleanup the orphan list in
- * ext4_handle_inode_extension(). Do it now.
+ * If i_disksize got extended either due to writeback of delalloc
+ * blocks or extending truncate while the DIO was running we could fail
+ * to cleanup the orphan list in ext4_handle_inode_extension(). Do it
+ * now.
*/
if (!list_empty(&EXT4_I(inode)->i_orphan) && inode->i_nlink) {
handle_t *handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
@@ -386,10 +387,11 @@ static int ext4_dio_write_end_io(struct kiocb *iocb, ssize_t size,
* blocks. But the code in ext4_iomap_alloc() is careful to use
* zeroed/unwritten extents if this is possible; thus we won't leave
* uninitialized blocks in a file even if we didn't succeed in writing
- * as much as we intended.
+ * as much as we intended. Also we can race with truncate or write
+ * expanding the file so we have to be a bit careful here.
*/
- WARN_ON_ONCE(i_size_read(inode) < READ_ONCE(EXT4_I(inode)->i_disksize));
- if (pos + size <= READ_ONCE(EXT4_I(inode)->i_disksize))
+ if (pos + size <= READ_ONCE(EXT4_I(inode)->i_disksize) &&
+ pos + size <= i_size_read(inode))
return size;
return ext4_handle_inode_extension(inode, pos, size);
}
