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

On Tue, Aug 04, 2026 at 12:41:13PM +0200, Jan Kara wrote:
> 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]>
> ---

Hey Jan, yes makese sense and it is fixing the issue for me. Feel free
to add:

Reviewed-by: Ojaswin Mujoo <[email protected]>

Regards,
ojaswin


>  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
>