From: Marco Elver <elver@google.com>
Date: Wed, 5 May 2021 01:40:24 +0000 (-0700)
Subject: kfence: maximize allocation wait timeout duration
X-Git-Tag: accepted/tizen/unified/20230118.172025~7280^2~1
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=37c9284f6932b915043717703d6496dfd59c85f5;p=platform%2Fkernel%2Flinux-rpi.git

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:

  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.

Link: https://lkml.kernel.org/r/20210421105132.3965998-3-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Jann Horn <jannh@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 235d726..9742649 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);