From: Marco Elver elver@google.com
commit 37c9284f6932b915043717703d6496dfd59c85f5 upstream.
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+05kMBXb4c0cXMS7Qi5NAJi...
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/kfence/core.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
--- 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> @@ -620,7 +621,16 @@ static void toggle_allocation_gate(struc /* 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);