[Devel] [PATCH] mm: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance_workfn()

[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.

Accepted in ms: https://lkml.org/lkml/2018/3/14/351
Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 mm/percpu.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index b15513d4a101..2cac240c015c 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -894,8 +894,12 @@ 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) {
+		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);