We got a WARNING in ext4_add_complete_io:
==================================================================
WARNING: at fs/ext4/page-io.c:231 ext4_put_io_end_defer+0x182/0x250
CPU: 10 PID: 77 Comm: ksoftirqd/10 Tainted: 6.3.0-rc2 #85
RIP: 0010:ext4_put_io_end_defer+0x182/0x250 [ext4]
[...]
Call Trace:
<TASK>
ext4_end_bio+0xa8/0x240 [ext4]
bio_endio+0x195/0x310
blk_update_request+0x184/0x770
scsi_end_request+0x2f/0x240
scsi_io_completion+0x75/0x450
scsi_finish_command+0xef/0x160
scsi_complete+0xa3/0x180
blk_complete_reqs+0x60/0x80
blk_done_softirq+0x25/0x40
__do_softirq+0x119/0x4c8
run_ksoftirqd+0x42/0x70
smpboot_thread_fn+0x136/0x3c0
kthread+0x140/0x1a0
ret_from_fork+0x2c/0x50
==================================================================
Above issue may happen as follows:
cpu1 cpu2
----------------------------|----------------------------
mount -o dioread_lock
ext4_writepages
ext4_do_writepages
*if (ext4_should_dioread_nolock(inode))*
// rsv_blocks is not assigned here
mount -o remount,dioread_nolock
ext4_journal_start_with_reserve
__ext4_journal_start
__ext4_journal_start_sb
jbd2__journal_start
*if (rsv_blocks)*
// h_rsv_handle is not initialized here
mpage_map_and_submit_extent
mpage_map_one_extent
dioread_nolock = ext4_should_dioread_nolock(inode)
if (dioread_nolock && (map->m_flags & EXT4_MAP_UNWRITTEN))
mpd->io_submit.io_end->handle = handle->h_rsv_handle
ext4_set_io_unwritten_flag
io_end->flag |= EXT4_IO_END_UNWRITTEN
// now io_end->handle is NULL but has EXT4_IO_END_UNWRITTEN flag
scsi_finish_command
scsi_io_completion
scsi_io_completion_action
scsi_end_request
blk_update_request
req_bio_endio
bio_endio
bio->bi_end_io > ext4_end_bio
ext4_put_io_end_defer
ext4_add_complete_io
// trigger WARN_ON(!io_end->handle && sbi->s_journal);
The immediate cause of this problem is that ext4_should_dioread_nolock()
function returns inconsistent values in the ext4_do_writepages() and
mpage_map_one_extent(). There are four conditions in this function that
can be changed at mount time to cause this problem. These four conditions
can be divided into two categories:
(1) journal_data and EXT4_EXTENTS_FL, which can be changed by ioctl
(2) DELALLOC and DIOREAD_NOLOCK, which can be changed by remount
The two in the first category have been fixed by commit c8585c6fcaf2
("ext4: fix races between changing inode journal mode and ext4_writepages")
and commit cb85f4d23f79 ("ext4: fix race between writepages and enabling
EXT4_EXTENTS_FL") respectively.
Two cases in the other category have not yet been fixed, and the above
issue is caused by this situation. We refer to the fix for the first
category, when applying options during remount, we grab s_writepages_rwsem
to avoid racing with writepages ops to trigger this problem.
Fixes: 6b523df4fb5a ("ext4: use transaction reservation for extent conversion in ext4_end_io")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
V1->V2:
Grab s_writepages_rwsem unconditionally during remount.
Remove patches 1,2 that are no longer needed.
fs/ext4/ext4.h | 3 ++-
fs/ext4/super.c | 9 +++++++++
2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 9b2cfc32cf78..5f5ee0c20673 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1703,7 +1703,8 @@ struct ext4_sb_info {
/*
* Barrier between writepages ops and changing any inode's JOURNAL_DATA
- * or EXTENTS flag.
+ * or EXTENTS flag or between writepages ops and changing DELALLOC or
+ * DIOREAD_NOLOCK mount options on remount.
*/
struct percpu_rw_semaphore s_writepages_rwsem;
struct dax_device *s_daxdev;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e6d84c1e34a4..607ebf2a008b 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -6403,7 +6403,16 @@ static int __ext4_remount(struct fs_context *fc, struct super_block *sb)
}
+ /*
+ * Changing the DIOREAD_NOLOCK or DELALLOC mount options may cause
+ * two calls to ext4_should_dioread_nolock() to return inconsistent
+ * values, triggering WARN_ON in ext4_add_complete_io(). we grab
+ * here s_writepages_rwsem to avoid race between writepages ops and
+ * remount.
+ */
+ percpu_down_write(&sbi->s_writepages_rwsem);
ext4_apply_options(fc, sb);
+ percpu_up_write(&sbi->s_writepages_rwsem);
if ((old_opts.s_mount_opt & EXT4_MOUNT_JOURNAL_CHECKSUM) ^
test_opt(sb, JOURNAL_CHECKSUM)) {
--
2.31.1
