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Subject[28/35] PM / Hibernate: Fix free_unnecessary_pages()
2.6.33-longterm review patch.  If anyone has any objections, please let us know.


From: "Rafael J. Wysocki" <>

commit 4d4cf23cdde2f8f9324f5684a7f349e182039529 upstream.

There is a bug in free_unnecessary_pages() that causes it to
attempt to free too many pages in some cases, which triggers the
BUG_ON() in memory_bm_clear_bit() for copy_bm. Namely, if
count_data_pages() is initially greater than alloc_normal, we get
to_free_normal equal to 0 and "save" greater from 0. In that case,
if the sum of "save" and count_highmem_pages() is greater than
alloc_highmem, we subtract a positive number from to_free_normal.
Hence, since to_free_normal was 0 before the subtraction and is
an unsigned int, the result is converted to a huge positive number
that is used as the number of pages to free.

Fix this bug by checking if to_free_normal is actually greater
than or equal to the number we're going to subtract from it.

Signed-off-by: Rafael J. Wysocki <>
Reported-and-tested-by: Matthew Garrett <>
Signed-off-by: Greg Kroah-Hartman <>

kernel/power/snapshot.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1193,7 +1193,11 @@ static void free_unnecessary_pages(void)
to_free_highmem = alloc_highmem - save;
} else {
to_free_highmem = 0;
- to_free_normal -= save - alloc_highmem;
+ save -= alloc_highmem;
+ if (to_free_normal > save)
+ to_free_normal -= save;
+ else
+ to_free_normal = 0;


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