xfs: check for dead buffers in xfs_buf_find_insert

commit 07eae0fa67ca4bbb199ad85645e0f9dfaef931cd upstream.

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>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Cc: stable@vger.kernel.org # v6.0
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index aa63b8efd7822856ba85407a810ad7963a551a9c..b9444ff5c8a5865a1b84591f7718316713f851f6 100644 (file)
--- a/fs/xfs/xfs_buf.c
+++ b/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)