mm: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance_workfn()

In case of memory deficit and low percpu memory pages,
pcpu_balance_workfn() takes pcpu_alloc_mutex for a long
time (as it makes memory allocations itself and waits
for memory reclaim). If tasks doing pcpu_alloc() are
choosen by OOM killer, they can't exit, because they
are waiting for the mutex.

The patch makes pcpu_alloc() to care about killing signal
and use mutex_lock_killable(), when it's allowed by GFP
flags. This guarantees, a task does not miss SIGKILL
from OOM killer.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 11 insertions, 2 deletions

diff --git a/mm/percpu.c b/mm/percpu.c
index 15a398c00791..9297098519a6 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1373,8 +1373,17 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
                 return NULL;
         }
 
-        if (!is_atomic)
-                mutex_lock(&pcpu_alloc_mutex);
+        if (!is_atomic) {
+                /*
+                 * pcpu_balance_workfn() allocates memory under this mutex,
+                 * and it may wait for memory reclaim. Allow current task
+                 * to become OOM victim, in case of memory pressure.
+                 */
+                if (gfp & __GFP_NOFAIL)
+                        mutex_lock(&pcpu_alloc_mutex);
+                else if (mutex_lock_killable(&pcpu_alloc_mutex))
+                        return NULL;
+        }
 
         spin_lock_irqsave(&pcpu_lock, flags);