[PATCH] ext4: Avoid entering writeback paths during fastcommit replay

Fastcommit replay effectively happens in nojournal mode. This results in
ext4_mark_iloc_dirty() setting I_METADATA_WRITEBACK flag and as a result
we end up entering filesystem writeback functions. However during
fastcommit replay s_writepages_rwsem isn't initialized yet and hence we
crash.

Fix the problem by avoiding setting I_METADATA_WRITEBACK during
fastcommit replay. Journal replay flushes the whole block device after
replay anyway so all metadata is properly persisted and replay is faster
this way as a bonus.

Fixes: c26339e1df33 ("ext4: Fix data integrity writeout issues in nojournal mode")
Reported-by: Venkat Rao Bagalkote <[email protected]>
Reported-by: Ojaswin Mujoo <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
---
 fs/ext4/inode.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

Christian, please add this fixup to my sync fixing series. Thanks!

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 7a1f961cd11c..12ff84ab5741 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -6408,9 +6408,10 @@ int ext4_chunk_trans_blocks(struct inode *inode, int nrblocks)
 int ext4_mark_iloc_dirty(handle_t *handle,
 			 struct inode *inode, struct ext4_iloc *iloc)
 {
+	struct super_block *sb = inode->i_sb;
 	int err = 0;
 
-	err = ext4_emergency_state(inode->i_sb);
+	err = ext4_emergency_state(sb);
 	if (unlikely(err)) {
 		put_bh(iloc->bh);
 		return err;
@@ -6425,9 +6426,13 @@ int ext4_mark_iloc_dirty(handle_t *handle,
 	put_bh(iloc->bh);
 	/*
 	 * Mark that there's metadata writeout pending for the inode so that it
-	 * gets properly flushed on fsync(2) and similar.
+	 * gets properly flushed on fsync(2) and similar. We don't bother for
+	 * fastcommit replay as that flushes the whole bdev afterwards anyway.
+	 * It is faster this way and we avoid entering fs writeback paths which
+	 * aren't fully initialized yet.
 	 */
-	if (!EXT4_SB(inode->i_sb)->s_journal) {
+	if (!ext4_handle_valid(handle) &&
+	    !(EXT4_SB(sb)->s_mount_state & EXT4_FC_REPLAY)) {
 		/*
 		 * Inode didn't need to go through dirtying, make sure it is
 		 * attached to wb so that writeback can handle it.
-- 
2.51.0