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().
Reported-by: syzbot+aacb82fca60873422114@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/ext4/mmp.c | 30 +++++++++++++++++++++---------
1 file changed, 21 insertions(+), 9 deletions(-)
diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index 4681fff6665f..46735ce315b5 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.
@@ -340,7 +348,11 @@ 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;
--
2.35.3
