From 737449236240e30a7bbe99f4d5586b8ed1416763 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Tue, 31 Jul 2012 16:45:20 -0700 Subject: [PATCH] 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 Signed-off-by: Mel Gorman Acked-by: Rik van Riel Cc: Christoph Hellwig Cc: David S. Miller Cc: Eric B Munson Cc: Eric Paris Cc: James Morris Cc: Mel Gorman Cc: Mike Christie Cc: Neil Brown Cc: Peter Zijlstra Cc: Sebastian Andrzej Siewior Cc: Trond Myklebust Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swapfile.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index 7307fc928d7b..63958d60ecb0 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -549,7 +549,6 @@ static unsigned char swap_entry_free(struct swap_info_struct *p, /* 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 @@ static unsigned char swap_entry_free(struct swap_info_struct *p, 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; -- 2.20.1