[PATCH] xfs: do not call xfs_buf_hash_destroy on a NULL pag

[Colin King <colin.king@canonical.com>]

From: Colin Ian King <colin.king@canonical.com>

If pag cannot be allocated, the current error exit path will trip
a null pointer deference error when calling xfs_buf_hash_destroy
with a null pag.  Fix this by adding a new error exit lable and
jumping to this, avoiding the hash destroy and unnecessary kmem_free
on pag.

Fixes CoverityScan CID#1397628 ("Dereference after null check")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 fs/xfs/xfs_mount.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 9b9540d..4e66cd19 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -207,7 +207,7 @@ xfs_initialize_perag(
 
 		pag = kmem_zalloc(sizeof(*pag), KM_MAYFAIL);
 		if (!pag)
-			goto out_unwind;
+			goto out_unwind_pags;
 		pag->pag_agno = index;
 		pag->pag_mount = mp;
 		spin_lock_init(&pag->pag_ici_lock);
@@ -242,6 +242,7 @@ xfs_initialize_perag(
 out_unwind:
 	xfs_buf_hash_destroy(pag);
 	kmem_free(pag);
+out_unwind_pags:
 	for (; index > first_initialised; index--) {
 		pag = radix_tree_delete(&mp->m_perag_tree, index);
 		xfs_buf_hash_destroy(pag);
-- 
2.10.2