Commit 73744923 authored Jul 31, 2012 by Mel Gorman Committed by Linus Torvalds Jul 31, 2012

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 <dfeng@redhat.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric B Munson <emunson@mgebm.net>
Cc: Eric Paris <eparis@redhat.com>
Cc: James Morris <jmorris@namei.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 192e501b

mm/swapfile.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -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;

Admin message