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Commit 2b45ab33 authored by David Rientjes's avatar David Rientjes Committed by Linus Torvalds
Browse files

oom: fix constraint deadlock 



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

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

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 <ak@suse.de>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Christoph Lameter <clameter@engr.sgi.com>
Cc: Martin J. Bligh <mbligh@mbligh.org>
Signed-off-by: default avatarDavid Rientjes <rientjes@google.com>
Cc: <stable@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2b744c01

mm/oom_kill.c

+6 −4
Original line number Diff line number Diff line
@@ -399,6 +399,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) 
	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)
@@ -416,14 +417,15 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) 
	if (sysctl_panic_on_oom == 2)

		panic("out of memory. Compulsory panic_on_oom is selected.\n");



	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) {

	case CONSTRAINT_MEMORY_POLICY:

		oom_kill_process(current, points,

				"No available memory (MPOL_BIND)");