linux-kernel - [PATCH v2 2/3] kfence: maximize allocation wait timeout duration

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Date:   Wed, 21 Apr 2021 12:51:31 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, akpm@...ux-foundation.org
Cc:     glider@...gle.com, dvyukov@...gle.com, jannh@...gle.com,
        mark.rutland@....com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, kasan-dev@...glegroups.com, hdanton@...a.com
Subject: [PATCH v2 2/3] kfence: maximize allocation wait timeout duration

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@...gle.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 235d726f88bc..9742649f3f88 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>
@@ -621,7 +622,16 @@ static void toggle_allocation_gate(struct work_struct *work)
 	/* Enable static key, and await allocation to happen. */
 	static_branch_enable(&kfence_allocation_key);
 
-	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));
+	}
 
 	/* Disable static key and reset timer. */
 	static_branch_disable(&kfence_allocation_key);
-- 
2.31.1.368.gbe11c130af-goog