[PATCH] mm: avoid livelock on !__GFP_FS allocations

[Mel Gorman]

This patch seems to have gotten lost in the cracks and the discussion
on alternatives that started here https://lkml.org/lkml/2011/10/25/24
petered out without any alternative patches being posted. Lacking
a viable alternative patch, I'm reposting this patch because AFAIK,
this bug still exists.

Colin Cross reported;

  Under the following conditions, __alloc_pages_slowpath can loop forever:
  gfp_mask & __GFP_WAIT is true
  gfp_mask & __GFP_FS is false
  reclaim and compaction make no progress
  order <= PAGE_ALLOC_COSTLY_ORDER

  These conditions happen very often during suspend and resume,
  when pm_restrict_gfp_mask() effectively converts all GFP_KERNEL
  allocations into __GFP_WAIT.

  The oom killer is not run because gfp_mask & __GFP_FS is false,
  but should_alloc_retry will always return true when order is less
  than PAGE_ALLOC_COSTLY_ORDER.

In his fix, he avoided retrying the allocation if reclaim made no
progress and __GFP_FS was not set. The problem is that this would
result in GFP_NOIO allocations failing that previously succeeded
which would be very unfortunate.

The big difference between GFP_NOIO and suspend converting GFP_KERNEL
to behave like GFP_NOIO is that normally flushers will be cleaning
pages and kswapd reclaims pages allowing GFP_NOIO to succeed after
a short delay. The same does not necessarily apply during suspend as
the storage device may be suspended.  Hence, this patch special cases
the suspend case to fail the page allocation if reclaim cannot make
progress. This might cause suspend to abort but that is better than
a livelock.

[mgorman@xxxxxxx: Rework fix to be suspend specific]
Reported-and-tested-by: Colin Cross <ccross@xxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
 mm/page_alloc.c |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9dd443d..5402897 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -127,6 +127,20 @@ void pm_restrict_gfp_mask(void)
 	saved_gfp_mask = gfp_allowed_mask;
 	gfp_allowed_mask &= ~GFP_IOFS;
 }
+
+static bool pm_suspending(void)
+{
+	if ((gfp_allowed_mask & GFP_IOFS) == GFP_IOFS)
+		return false;
+	return true;
+}
+
+#else
+
+static bool pm_suspending(void)
+{
+	return false;
+}
 #endif /* CONFIG_PM_SLEEP */
 
 #ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
@@ -2214,6 +2228,14 @@ rebalance:
 
 			goto restart;
 		}
+
+		/*
+		 * Suspend converts GFP_KERNEL to __GFP_WAIT which can
+		 * prevent reclaim making forward progress without
+		 * invoking OOM. Bail if we are suspending
+		 */
+		if (pm_suspending())
+			goto nopage;
 	}
 
 	/* Check if we should retry the allocation */
--
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