[PATCH] xfs: shutdown filesystem if xfs_perag_get fails

[Mark Tinguely <tinguely@xxxxxxx>]

This problem happened locally with a bad inode number from xfs
recovery. xfs_perag_get() can return NULL if given a bad agno.
Most callers of xfs_perag_get() do not check for a NULL before
using the pointer. This patch forces a shutdown of the filesystem
for those callers that do not check the return value rather than
crashing on a dereferenced NULL pointer.

Signed-off-by: Mark Tinguely <tinguely@xxxxxxx>
---
 fs/xfs/xfs_icache.c |    2 +-
 fs/xfs/xfs_mount.c  |    4 ++--
 fs/xfs/xfs_mount.h  |   17 ++++++++++++++++-
 3 files changed, 19 insertions(+), 4 deletions(-)

Index: b/fs/xfs/xfs_icache.c
===================================================================
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -656,7 +656,7 @@ xfs_inode_ag_iterator(
        xfs_agnumber_t          ag;
 
        ag = 0;
-       while ((pag = xfs_perag_get(mp, ag))) {
+       while ((pag = __xfs_perag_get(mp, ag))) {
                ag = pag->pag_agno + 1;
                error = xfs_inode_ag_walk(mp, pag, execute, flags, args, -1);
                xfs_perag_put(pag);
Index: b/fs/xfs/xfs_mount.c
===================================================================
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -193,7 +193,7 @@ xfs_uuid_unmount(
  * have to protect against changes is the tree structure itself.
  */
 struct xfs_perag *
-xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
+__xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
 {
        struct xfs_perag        *pag;
        int                     ref = 0;
@@ -442,7 +442,7 @@ xfs_initialize_perag(
         * AGs we don't find ready for initialisation.
         */
        for (index = 0; index < agcount; index++) {
-               pag = xfs_perag_get(mp, index);
+               pag = __xfs_perag_get(mp, index);
                if (pag) {
                        xfs_perag_put(pag);
                        continue;
Index: b/fs/xfs/xfs_mount.h
===================================================================
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -336,12 +336,27 @@ xfs_daddr_to_agbno(struct xfs_mount *mp,
 /*
  * perag get/put wrappers for ref counting
  */
-struct xfs_perag *xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno);
+struct xfs_perag *__xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno);
 struct xfs_perag *xfs_perag_get_tag(struct xfs_mount *mp, xfs_agnumber_t agno,
                                        int tag);
 void   xfs_perag_put(struct xfs_perag *pag);
 
 /*
+ * Ensure the per AG entry was found. Shutting down the filesystem
+ * is better than crashing the OS.
+ */
+static inline struct xfs_perag *
+xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
+{
+       struct xfs_perag        *pag;
+
+       pag = __xfs_perag_get(mp, agno);
+       if (!pag)
+               xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
+       return pag;
+}
+
+/*
  * Per-cpu superblock locking functions
  */
 #ifdef HAVE_PERCPU_SB