path: root/kernel
diff options
authorMichal Hocko <mhocko@suse.cz>2014-10-20 18:12:32 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-11-14 08:47:58 -0800
commite033782a2669ae60db31d28127974bac18c63e33 (patch)
treebb4db15f0061433565e49b87804ea64badea0f41 /kernel
parentf95ad6ed20948dee0a7c1472250b530136f75db3 (diff)
OOM, PM: OOM killed task shouldn't escape PM suspend
commit 5695be142e203167e3cb515ef86a88424f3524eb upstream. PM freezer relies on having all tasks frozen by the time devices are getting frozen so that no task will touch them while they are getting frozen. But OOM killer is allowed to kill an already frozen task in order to handle OOM situtation. In order to protect from late wake ups OOM killer is disabled after all tasks are frozen. This, however, still keeps a window open when a killed task didn't manage to die by the time freeze_processes finishes. Reduce the race window by checking all tasks after OOM killer has been disabled. This is still not race free completely unfortunately because oom_killer_disable cannot stop an already ongoing OOM killer so a task might still wake up from the fridge and get killed without freeze_processes noticing. Full synchronization of OOM and freezer is, however, too heavy weight for this highly unlikely case. Introduce and check oom_kills counter which gets incremented early when the allocator enters __alloc_pages_may_oom path and only check all the tasks if the counter changes during the freezing attempt. The counter is updated so early to reduce the race window since allocator checked oom_killer_disabled which is set by PM-freezing code. A false positive will push the PM-freezer into a slow path but that is not a big deal. Changes since v1 - push the re-check loop out of freeze_processes into check_frozen_processes and invert the condition to make the code more readable as per Rafael Fixes: f660daac474c6f (oom: thaw threads if oom killed thread is frozen before deferring) Signed-off-by: Michal Hocko <mhocko@suse.cz> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
1 files changed, 39 insertions, 1 deletions
diff --git a/kernel/power/process.c b/kernel/power/process.c
index 1b212bee1510..0695319b5fde 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -103,6 +103,28 @@ static int try_to_freeze_tasks(bool user_only)
return todo ? -EBUSY : 0;
+ * Returns true if all freezable tasks (except for current) are frozen already
+ */
+static bool check_frozen_processes(void)
+ struct task_struct *g, *p;
+ bool ret = true;
+ read_lock(&tasklist_lock);
+ for_each_process_thread(g, p) {
+ if (p != current && !freezer_should_skip(p) &&
+ !frozen(p)) {
+ ret = false;
+ goto done;
+ }
+ }
+ read_unlock(&tasklist_lock);
+ return ret;
* freeze_processes - Signal user space processes to enter the refrigerator.
@@ -111,6 +133,7 @@ static int try_to_freeze_tasks(bool user_only)
int freeze_processes(void)
int error;
+ int oom_kills_saved;
error = __usermodehelper_disable(UMH_FREEZING);
if (error)
@@ -121,12 +144,27 @@ int freeze_processes(void)
printk("Freezing user space processes ... ");
pm_freezing = true;
+ oom_kills_saved = oom_kills_count();
error = try_to_freeze_tasks(true);
if (!error) {
- printk("done.");
+ /*
+ * There might have been an OOM kill while we were
+ * freezing tasks and the killed task might be still
+ * on the way out so we have to double check for race.
+ */
+ if (oom_kills_count() != oom_kills_saved &&
+ !check_frozen_processes()) {
+ __usermodehelper_set_disable_depth(UMH_ENABLED);
+ printk("OOM in progress.");
+ error = -EBUSY;
+ goto done;
+ }
+ printk("done.");