+ kfence-maximize-allocation-wait-timeout-duration.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: kfence: maximize allocation wait timeout duration
has been added to the -mm tree.  Its filename is
     kfence-maximize-allocation-wait-timeout-duration.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/kfence-maximize-allocation-wait-timeout-duration.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/kfence-maximize-allocation-wait-timeout-duration.patch

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------------------------------------------------------
From: Marco Elver <elver@google.com>
Subject: 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.

Link: https://lkml.kernel.org/r/20210419085027.761150-3-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>
---

 mm/kfence/core.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/mm/kfence/core.c~kfence-maximize-allocation-wait-timeout-duration
+++ a/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(struc
 
 	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. */
_

Patches currently in -mm which might be from elver@google.com are

kfence-zero-guard-page-after-out-of-bounds-access.patch
kfence-await-for-allocation-using-wait_event.patch
kfence-maximize-allocation-wait-timeout-duration.patch
kfence-use-power-efficient-work-queue-to-run-delayed-work.patch