xfs: check for dead buffers in xfs_buf_find_insert

commit 07eae0f upstream.

Commit 32dd4f9 ("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: 32dd4f9 ("xfs: remove a superflous hash lookup when inserting new buffers")
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Dave Chinner <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Cc: [email protected] # v6.0
Signed-off-by: Carlos Maiolino <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Christoph Hellwig

fs/xfs/xfs_buf.c

@@ -663,9 +663,8 @@ 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)