Re: [PATCH v2 2/3] kfence: maximize allocation wait timeout duration

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Hi Marco,

We found kfence_test will fails  on ARM64 with this patch with/without  CONFIG_DETECT_HUNG_TASK,

Any thought ?


On 2021/9/16 9:02, Kefeng Wang wrote:

On 2021/4/21 18:51, Marco Elver wrote:
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@xxxxxxxxxxxxxx

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

Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
---
  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);





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