Re: [PATCH 1/3] jbd2: use READ_ONCE for lockless jinode reads

[Jan Kara]

On Fri 30-01-26 11:12:30, Li Chen wrote:
> jbd2_inode fields are updated under journal->j_list_lock, but some
> paths read them without holding the lock (e.g. fast commit
> helpers and the ordered truncate fast path).
> 
> Use READ_ONCE() for these lockless reads to correct the
> concurrency assumptions.
> 
> Suggested-by: Jan Kara <jack@xxxxxxxx>
> Signed-off-by: Li Chen <me@linux.beauty>

Just one nit below. With that fixed feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

> @@ -191,12 +197,30 @@ EXPORT_SYMBOL(jbd2_submit_inode_data);
>  
>  int jbd2_wait_inode_data(journal_t *journal, struct jbd2_inode *jinode)
>  {
> -	if (!jinode || !(jinode->i_flags & JI_WAIT_DATA) ||
> -		!jinode->i_vfs_inode || !jinode->i_vfs_inode->i_mapping)
> +	struct address_space *mapping;
> +	struct inode *inode;
> +	unsigned long flags;
> +	loff_t start, end;
> +
> +	if (!jinode)
> +		return 0;
> +
> +	flags = READ_ONCE(jinode->i_flags);
> +	if (!(flags & JI_WAIT_DATA))
> +		return 0;
> +
> +	inode = READ_ONCE(jinode->i_vfs_inode);

i_vfs_inode never changes so READ_ONCE is pointless here.

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR