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Commit 4743f839 authored by Pranay Kr. Srivastava's avatar Pranay Kr. Srivastava Committed by Theodore Ts'o
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ext4: Fix WARN_ON_ONCE in ext4_commit_super() 



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: default avatarPranay Kr. Srivastava <pranjas@gmail.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 646caa9c

fs/ext4/super.c

+16 −14
Original line number Diff line number Diff line
@@ -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);