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Subject[patch 14/69] oom: fix constraint deadlock
-stable review patch.  If anyone has any objections, please let us know.

From: David Rientjes <>

Fixes a deadlock in the OOM killer for allocations that are not

Before the OOM killer checks for the allocation constraint, it takes

constrained_alloc() iterates through each zone in the allocation zonelist
and calls cpuset_zone_allowed_softwall() to determine whether an allocation
for gfp_mask is possible. If a zone's node is not in the OOM-triggering
task's mems_allowed, it is not exiting, and we did not fail on a
__GFP_HARDWALL allocation, cpuset_zone_allowed_softwall() attempts to take
callback_mutex to check the nearest exclusive ancestor of current's cpuset.
This results in deadlock.

We now take callback_mutex after iterating through the zonelist since we
don't need it yet.

Cc: Andi Kleen <>
Cc: Nick Piggin <>
Cc: Christoph Lameter <>
Cc: Martin J. Bligh <>
Signed-off-by: David Rientjes <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Chris Wright <>

mm/oom_kill.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- linux-
+++ linux-
@@ -397,6 +397,7 @@ void out_of_memory(struct zonelist *zone
struct task_struct *p;
unsigned long points = 0;
unsigned long freed = 0;
+ int constraint;

blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
if (freed > 0)
@@ -411,14 +412,15 @@ void out_of_memory(struct zonelist *zone

- cpuset_lock();
- read_lock(&tasklist_lock);
* Check if there were limitations on the allocation (only relevant for
* NUMA) that may require different handling.
- switch (constrained_alloc(zonelist, gfp_mask)) {
+ constraint = constrained_alloc(zonelist, gfp_mask);
+ cpuset_lock();
+ read_lock(&tasklist_lock);
+ switch (constraint) {
oom_kill_process(current, points,
"No available memory (MPOL_BIND)");
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