[PATCH 2/3] kfence: maximize allocation wait timeout duration

From: Marco Elver <elver@google.com>
To: elver@google.com, akpm@linux-foundation.org
Cc: glider@google.com, dvyukov@google.com, jannh@google.com,
	mark.rutland@arm.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, kasan-dev@googlegroups.com
Subject: [PATCH 2/3] kfence: maximize allocation wait timeout duration
Date: Mon, 19 Apr 2021 10:50:26 +0200	[thread overview]
Message-ID: <20210419085027.761150-3-elver@google.com> (raw)
In-Reply-To: <20210419085027.761150-1-elver@google.com>

The allocation wait timeout was initially added because of warnings due
to CONFIG_DETECT_HUNG_TASK=y [1]. While the 1 sec timeout is sufficient
to resolve the warnings (given the hung task timeout must be 1 sec or
larger) it may cause unnecessary wake-ups if the system is idle.
[1] https://lkml.kernel.org/r/CADYN=9J0DQhizAGB0-jz4HOBBh+05kMBXb4c0cXMS7Qi5NAJiw@mail.gmail.com

Fix it by computing the timeout duration in terms of the current
sysctl_hung_task_timeout_secs value.

Signed-off-by: Marco Elver <elver@google.com>
---
 mm/kfence/core.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 5f0a56041549..73e7b621fb36 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -20,6 +20,7 @@
 #include <linux/moduleparam.h>
 #include <linux/random.h>
 #include <linux/rcupdate.h>
+#include <linux/sched/sysctl.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
@@ -626,7 +627,16 @@ static void toggle_allocation_gate(struct work_struct *work)
 
 	WRITE_ONCE(kfence_timer_waiting, true);
 	smp_mb(); /* See comment in __kfence_alloc(). */
-	wait_event_timeout(allocation_wait, atomic_read(&kfence_allocation_gate), HZ);
+	if (sysctl_hung_task_timeout_secs) {
+		/*
+		 * During low activity with no allocations we might wait a
+		 * while; let's avoid the hung task warning.
+		 */
+		wait_event_timeout(allocation_wait, atomic_read(&kfence_allocation_gate),
+				   sysctl_hung_task_timeout_secs * HZ / 2);
+	} else {
+		wait_event(allocation_wait, atomic_read(&kfence_allocation_gate));
+	}
 	smp_store_release(&kfence_timer_waiting, false); /* Order after wait_event(). */
 
 	/* Disable static key and reset timer. */
-- 
2.31.1.368.gbe11c130af-goog

