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ext4: Fix WARN_ON_ONCE in ext4_commit_super()

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If there are racing calls to ext4_commit_super() it's possible for
another writeback of the superblock to result in the buffer being
marked with an error after we check if the buffer is marked as having
a write error and the buffer up-to-date flag is set again.  If that
happens mark_buffer_dirty() can end up throwing a WARN_ON_ONCE.

Fix this by moving this check to write before we call
write_buffer_dirty(), and keeping the buffer locked during this whole
sequence.

Signed-off-by: Pranay Kr. Srivastava <pranjas@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Pranay Kr. Srivastava 2016-07-04 10:24:52 -04:00 committed by Theodore Ts'o
parent 646caa9c8e
commit 4743f83990
1 changed files with 16 additions and 14 deletions
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30
fs/ext4/super.c
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@ -4327,20 +4327,6 @@ static int ext4_commit_super(struct super_block *sb, int sync)
if (!sbh || block_device_ejected(sb))
return error;
if (buffer_write_io_error(sbh)) {
/*
* Oh, dear. A previous attempt to write the
* superblock failed. This could happen because the
* USB device was yanked out. Or it could happen to
* be a transient write error and maybe the block will
* be remapped. Nothing we can do but to retry the
* write and hope for the best.
*/
ext4_msg(sb, KERN_ERR, "previous I/O error to "
"superblock detected");
clear_buffer_write_io_error(sbh);
set_buffer_uptodate(sbh);
}
/*
* If the file system is mounted read-only, don't update the
* superblock write time. This avoids updating the superblock
@ -4371,7 +4357,23 @@ static int ext4_commit_super(struct super_block *sb, int sync)
&EXT4_SB(sb)->s_freeinodes_counter));
BUFFER_TRACE(sbh, "marking dirty");
ext4_superblock_csum_set(sb);
lock_buffer(sbh);
if (buffer_write_io_error(sbh)) {
/*
* Oh, dear. A previous attempt to write the
* superblock failed. This could happen because the
* USB device was yanked out. Or it could happen to
* be a transient write error and maybe the block will
* be remapped. Nothing we can do but to retry the
* write and hope for the best.
*/
ext4_msg(sb, KERN_ERR, "previous I/O error to "
"superblock detected");
clear_buffer_write_io_error(sbh);
set_buffer_uptodate(sbh);
}
mark_buffer_dirty(sbh);
unlock_buffer(sbh);
if (sync) {
error = __sync_dirty_buffer(sbh,
test_opt(sb, BARRIER) ? WRITE_FUA : WRITE_SYNC);