[099/146] mm/page_alloc.c: prevent unending loop in

[Greg KH]

2.6.38-stable review patch.  If anyone has any objections, please let us know.

------------------
 __alloc_pages_slowpath()

From: Andrew Barry <abarry@xxxxxxxx>

commit cfa54a0fcfc1017c6f122b6f21aaba36daa07f71 upstream.

I believe I found a problem in __alloc_pages_slowpath, which allows a
process to get stuck endlessly looping, even when lots of memory is
available.

Running an I/O and memory intensive stress-test I see a 0-order page
allocation with __GFP_IO and __GFP_WAIT, running on a system with very
little free memory.  Right about the same time that the stress-test gets
killed by the OOM-killer, the utility trying to allocate memory gets stuck
in __alloc_pages_slowpath even though most of the systems memory was freed
by the oom-kill of the stress-test.

The utility ends up looping from the rebalance label down through the
wait_iff_congested continiously.  Because order=0,
__alloc_pages_direct_compact skips the call to get_page_from_freelist.
Because all of the reclaimable memory on the system has already been
reclaimed, __alloc_pages_direct_reclaim skips the call to
get_page_from_freelist.  Since there is no __GFP_FS flag, the block with
__alloc_pages_may_oom is skipped.  The loop hits the wait_iff_congested,
then jumps back to rebalance without ever trying to
get_page_from_freelist.  This loop repeats infinitely.

The test case is pretty pathological.  Running a mix of I/O stress-tests
that do a lot of fork() and consume all of the system memory, I can pretty
reliably hit this on 600 nodes, in about 12 hours.  32GB/node.

Signed-off-by: Andrew Barry <abarry@xxxxxxxx>
Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
Reviewed-by: Rik van Riel<riel@xxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 mm/page_alloc.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2044,6 +2044,7 @@ restart:
 		first_zones_zonelist(zonelist, high_zoneidx, NULL,
 					&preferred_zone);
 
+rebalance:
 	/* This is the last chance, in general, before the goto nopage. */
 	page = get_page_from_freelist(gfp_mask, nodemask, order, zonelist,
 			high_zoneidx, alloc_flags & ~ALLOC_NO_WATERMARKS,
@@ -2051,7 +2052,6 @@ restart:
 	if (page)
 		goto got_pg;
 
-rebalance:
 	/* Allocate without watermarks if the context allows */
 	if (alloc_flags & ALLOC_NO_WATERMARKS) {
 		page = __alloc_pages_high_priority(gfp_mask, order,


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