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 (file)
--- 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);