[PATCH 1/3] ext4: avoid kernel warning when writing the superblock to a dead device

[PATCH 1/3] ext4: avoid kernel warning when writing the superblock to a dead device

[Theodore Ts'o]

The xfstests generic/475 test switches the underlying device with
dm-error while running a stress test.  This results in a large number
of file system errors, and since we can't lock the buffer head when
marking the superblock dirty in the ext4_grp_locked_error() case, it's
possible the superblock to be !buffer_uptodate() without
buffer_write_io_error() being true.

We need to set buffer_uptodate() before we call mark_buffer_dirty() or
this will trigger a WARN_ON.  It's safe to do this since the
superblock must have been properly read into memory or the mount would
have been successful.  So if buffer_uptodate() is not set, we can
safely assume that this happened due to a failed attempt to write the
superblock.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
---
 fs/ext4/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d6c142d73d99..fb12d3c17c1b 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4902,7 +4902,7 @@ static int ext4_commit_super(struct super_block *sb, int sync)
 	ext4_superblock_csum_set(sb);
 	if (sync)
 		lock_buffer(sbh);
-	if (buffer_write_io_error(sbh)) {
+	if (buffer_write_io_error(sbh) || !buffer_uptodate(sbh)) {
 		/*
 		 * Oh, dear.  A previous attempt to write the
 		 * superblock failed.  This could happen because the
-- 
2.19.1

Re: [PATCH 1/3] ext4: avoid kernel warning when writing the superblock to a dead device

[Sasha Levin]

Hi,

[This is an automated email]

This commit has been processed because it contains a -stable tag.
The stable tag indicates that it's relevant for the following trees: all

The bot has tested the following trees: v4.20.0, v4.19.13, v4.14.91, v4.9.148, v4.4.169, v3.18.131, 

v4.20.0: Build OK!
v4.19.13: Build OK!
v4.14.91: Build OK!
v4.9.148: Build OK!
v4.4.169: Failed to apply! Possible dependencies:
    1566a48aaa10 ("ext4: don't lock buffer in ext4_commit_super if holding spinlock")
    4743f8399061 ("ext4: Fix WARN_ON_ONCE in ext4_commit_super()")

v3.18.131: Failed to apply! Possible dependencies:
    1566a48aaa10 ("ext4: don't lock buffer in ext4_commit_super if holding spinlock")
    4743f8399061 ("ext4: Fix WARN_ON_ONCE in ext4_commit_super()")
    564bc402526e ("ext4, jbd2: add REQ_FUA flag when recording an error in the superblock")


How should we proceed with this patch?

--
Thanks,
Sasha