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Subject[PATCH v2] mm: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance_workfn()
From: Kirill Tkhai <>

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 <>
v2: Added explaining comment
mm/percpu.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index 50e7fdf84055..605e3228baa6 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1369,8 +1369,17 @@ 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);

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