Re: [PATCH 1/2] xfs: check for dead buffers in xfs_buf_find_insert

[Dave Chinner <david@fromorbit.com>]

On Mon, Jan 13, 2025 at 05:24:26AM +0100, Christoph Hellwig wrote:
> Commit 32dd4f9c506b ("xfs: remove a superflous hash lookup when inserting
> new buffers") converted xfs_buf_find_insert to use
> rhashtable_lookup_get_insert_fast and thus an operation that returns the
> existing buffer when an insert would duplicate the hash key.  But this
> code path misses the check for a buffer with a reference count of zero,
> which could lead to reusing an about to be freed buffer.  Fix this by
> using the same atomic_inc_not_zero pattern as xfs_buf_insert.
> 
> Fixes: 32dd4f9c506b ("xfs: remove a superflous hash lookup when inserting new buffers")
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/xfs_buf.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 6f313fbf7669..f80e39fde53b 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -664,9 +664,8 @@ xfs_buf_find_insert(
>  		spin_unlock(&bch->bc_lock);
>  		goto out_free_buf;
>  	}
> -	if (bp) {
> +	if (bp && atomic_inc_not_zero(&bp->b_hold)) {
>  		/* found an existing buffer */
> -		atomic_inc(&bp->b_hold);
>  		spin_unlock(&bch->bc_lock);
>  		error = xfs_buf_find_lock(bp, flags);
>  		if (error)

Looks good.

Reviewed-by: Dave Chinner <dchinner@redhat.com>

-- 
Dave Chinner
david@fromorbit.com