linux-kernel - [PATCH] percpu: Allow to kill tasks doing pcpu_alloc() and waiting for pcpu_balance

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Date:   Wed, 14 Mar 2018 14:51:48 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     akpm@...ux-foundation.org, tj@...nel.org, cl@...ux.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH] percpu: 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@...tuozzo.com>
---
 mm/percpu.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index 50e7fdf84055..212b4988926c 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1369,8 +1369,12 @@ 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);