The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y git checkout FETCH_HEAD git cherry-pick -x 949f95ff39bf188e594e7ecd8e29b82eb108f5bf # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2023051544-refold-dosage-6c5f@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^.. Possible dependencies: 949f95ff39bf ("ext4: fix lockdep warning when enabling MMP") 6810fad956df ("ext4: fix ext4_error_err save negative errno into superblock") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 949f95ff39bf188e594e7ecd8e29b82eb108f5bf Mon Sep 17 00:00:00 2001 From: Jan Kara <jack@xxxxxxx> Date: Tue, 11 Apr 2023 14:10:19 +0200 Subject: [PATCH] ext4: fix lockdep warning when enabling MMP When we enable MMP in ext4_multi_mount_protect() during mount or remount, we end up calling sb_start_write() from write_mmp_block(). This triggers lockdep warning because freeze protection ranks above s_umount semaphore we are holding during mount / remount. The problem is harmless because we are guaranteed the filesystem is not frozen during mount / remount but still let's fix the warning by not grabbing freeze protection from ext4_multi_mount_protect(). Cc: stable@xxxxxxxxxx Reported-by: syzbot+6b7df7d5506b32467149@xxxxxxxxxxxxxxxxxxxxxxxxx Link: https://syzkaller.appspot.com/bug?id=ab7e5b6f400b7778d46f01841422e5718fb81843 Signed-off-by: Jan Kara <jack@xxxxxxx> Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx> Link: https://lore.kernel.org/r/20230411121019.21940-1-jack@xxxxxxx Signed-off-by: Theodore Ts'o <tytso@xxxxxxx> diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c index 4022bc713421..0aaf38ffcb6e 100644 --- a/fs/ext4/mmp.c +++ b/fs/ext4/mmp.c @@ -39,28 +39,36 @@ static void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp) * Write the MMP block using REQ_SYNC to try to get the block on-disk * faster. */ -static int write_mmp_block(struct super_block *sb, struct buffer_head *bh) +static int write_mmp_block_thawed(struct super_block *sb, + struct buffer_head *bh) { struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data); - /* - * We protect against freezing so that we don't create dirty buffers - * on frozen filesystem. - */ - sb_start_write(sb); ext4_mmp_csum_set(sb, mmp); lock_buffer(bh); bh->b_end_io = end_buffer_write_sync; get_bh(bh); submit_bh(REQ_OP_WRITE | REQ_SYNC | REQ_META | REQ_PRIO, bh); wait_on_buffer(bh); - sb_end_write(sb); if (unlikely(!buffer_uptodate(bh))) return -EIO; - return 0; } +static int write_mmp_block(struct super_block *sb, struct buffer_head *bh) +{ + int err; + + /* + * We protect against freezing so that we don't create dirty buffers + * on frozen filesystem. + */ + sb_start_write(sb); + err = write_mmp_block_thawed(sb, bh); + sb_end_write(sb); + return err; +} + /* * Read the MMP block. It _must_ be read from disk and hence we clear the * uptodate flag on the buffer. @@ -344,7 +352,11 @@ int ext4_multi_mount_protect(struct super_block *sb, seq = mmp_new_seq(); mmp->mmp_seq = cpu_to_le32(seq); - retval = write_mmp_block(sb, bh); + /* + * On mount / remount we are protected against fs freezing (by s_umount + * semaphore) and grabbing freeze protection upsets lockdep + */ + retval = write_mmp_block_thawed(sb, bh); if (retval) goto failed;
