[PATCH RESEND] 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(-)

Hi Ted,

this has fallen through the cracks in VFS tree, now it applies cleanly to
Linus' tree so can you perhaps pick it up and push to Linus during the second
half of the merge window? 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