swapfile: avoid dereferencing bd_disk during swap_entry_free for network storage
Commit b3a27d ("swap: Add swap slot free callback to
block_device_operations") dereferences p->bdev->bd_disk but this is a NULL
dereference if using swap-over-NFS. This patch checks SWP_BLKDEV on the
swap_info_struct before dereferencing.
With reference to this callback, Christoph Hellwig stated "Please just
remove the callback entirely. It has no user outside the staging tree and
was added clearly against the rules for that staging tree". This would
also be my preference but there was not an obvious way of keeping zram in
staging/ happy.
Signed-off-by: Xiaotian Feng <[email protected]>
Signed-off-by: Mel Gorman <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Eric B Munson <[email protected]>
Cc: Eric Paris <[email protected]>
Cc: James Morris <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Mike Christie <[email protected]>
Cc: Neil Brown <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Trond Myklebust <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 7307fc9..63958d6 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -549,7 +549,6 @@
/* free if no reference */
if (!usage) {
- struct gendisk *disk = p->bdev->bd_disk;
if (offset < p->lowest_bit)
p->lowest_bit = offset;
if (offset > p->highest_bit)
@@ -560,9 +559,12 @@
nr_swap_pages++;
p->inuse_pages--;
frontswap_invalidate_page(p->type, offset);
- if ((p->flags & SWP_BLKDEV) &&
- disk->fops->swap_slot_free_notify)
- disk->fops->swap_slot_free_notify(p->bdev, offset);
+ if (p->flags & SWP_BLKDEV) {
+ struct gendisk *disk = p->bdev->bd_disk;
+ if (disk->fops->swap_slot_free_notify)
+ disk->fops->swap_slot_free_notify(p->bdev,
+ offset);
+ }
}
return usage;
