Re: [PATCH v2] erofs: fix refcount on the metabuf used for inode lookup

[Jingbo Xu]

On 2/22/24 5:03 AM, Sandeep Dhavale wrote:
> In erofs_find_target_block() when erofs_dirnamecmp() returns 0,
> we do not assign the target metabuf. This causes the caller
> erofs_namei()'s erofs_put_metabuf() at the end to be not effective
> leaving the refcount on the page.
> As the page from metabuf (buf->page) is never put, such page cannot be
> migrated or reclaimed. Fix it now by putting the metabuf from
> previous loop and assigning the current metabuf to target before
> returning so caller erofs_namei() can do the final put as it was
> intended.
> 
> Fixes: 500edd095648 ("erofs: use meta buffers for inode lookup")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sandeep Dhavale <dhavale@xxxxxxxxxx>


LGTM.

Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>


> ---
> Changes since v1
> - Rearrange the cases as suggested by Gao so there is less duplication
>     of the code and it is more readable
> 
>  fs/erofs/namei.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/erofs/namei.c b/fs/erofs/namei.c
> index d4f631d39f0f..f0110a78acb2 100644
> --- a/fs/erofs/namei.c
> +++ b/fs/erofs/namei.c
> @@ -130,24 +130,24 @@ static void *erofs_find_target_block(struct erofs_buf *target,
>  			/* string comparison without already matched prefix */
>  			diff = erofs_dirnamecmp(name, &dname, &matched);
>  
> -			if (!diff) {
> -				*_ndirents = 0;
> -				goto out;
> -			} else if (diff > 0) {
> -				head = mid + 1;
> -				startprfx = matched;
> -
> -				if (!IS_ERR(candidate))
> -					erofs_put_metabuf(target);
> -				*target = buf;
> -				candidate = de;
> -				*_ndirents = ndirents;
> -			} else {
> +			if (diff < 0) {
>  				erofs_put_metabuf(&buf);
> -
>  				back = mid - 1;
>  				endprfx = matched;
> +				continue;
> +			}
> +
> +			if (!IS_ERR(candidate))
> +				erofs_put_metabuf(target);
> +			*target = buf;
> +			if (!diff) {
> +				*_ndirents = 0;
> +				return de;
>  			}
> +			head = mid + 1;
> +			startprfx = matched;
> +			candidate = de;
> +			*_ndirents = ndirents;
>  			continue;
>  		}
>  out:		/* free if the candidate is valid */

-- 
Thanks,
Jingbo