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PM / Hibernate: Fix free_unnecessary_pages()

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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 <rjw@sisk.pl>
Reported-and-tested-by: Matthew Garrett <mjg@redhat.com>
Cc: stable@kernel.org
This commit is contained in:
Rafael J. Wysocki 2011-07-06 20:15:23 +02:00
parent a2fa83faf4
commit 4d4cf23cdd
1 changed files with 5 additions and 1 deletions
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6
kernel/power/snapshot.c
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@ -1211,7 +1211,11 @@ 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;
}
memory_bm_position_reset(&copy_bm);