3.16.61-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: "Pranay Kr. Srivastava" pranjas@gmail.com
commit 4743f83990614af6adb09ea7aa3c37b78c4031ab upstream.
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 Signed-off-by: Ben Hutchings ben@decadent.org.uk --- fs/ext4/super.c | 30 ++++++++++++++++-------------- 1 file changed, 16 insertions(+), 14 deletions(-)
--- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -4653,20 +4653,6 @@ static int ext4_commit_super(struct supe
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 @@ -4695,7 +4681,23 @@ static int ext4_commit_super(struct supe &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); if (error)