PM / Hibernate: Do not crash kernel in free_basic_memory_bitmaps()

I have received a report about the BUG_ON() in free_basic_memory_bitmaps()
triggering mysteriously during an aborted s2disk hibernation attempt.
The only way I can explain that is that /dev/snapshot was first
opened for writing (resume mode), then closed and then opened again
for reading and closed again without freezing tasks.  In that case
the first invocation of snapshot_open() would set the free_bitmaps
flag in snapshot_state, which is a static variable.  That flag
wouldn't be cleared later and the second invocation of snapshot_open()
would just leave it like that, so the subsequent snapshot_release()
would see data->frozen set and free_basic_memory_bitmaps() would be
called unnecessarily.

To prevent that from happening clear data->free_bitmaps in
snapshot_open() when the file is being opened for reading (hibernate
mode).

In addition to that, replace the BUG_ON() in free_basic_memory_bitmaps()
with a WARN_ON() as the kernel can continue just fine if the condition
checked by that macro occurs.

Fixes: aab172891542 (PM / hibernate: Fix user space driven resume regression)
Reported-by: Oliver Lorenz <olli@olorenz.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: 3.12+ <stable@vger.kernel.org> # 3.12+

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 98c3b34..ac2d1f6 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -792,7 +792,8 @@ void free_basic_memory_bitmaps(void)
 {
 	struct memory_bitmap *bm1, *bm2;
 
-	BUG_ON(!(forbidden_pages_map && free_pages_map));
+	if (WARN_ON(!(forbidden_pages_map && free_pages_map)))
+		return;
 
 	bm1 = forbidden_pages_map;
 	bm2 = free_pages_map;