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

From: David Laight <David.Laight@ACULAB.COM>
To: 'Kefeng Wang' <wangkefeng.wang@huawei.com>,
	Marco Elver <elver@google.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>
Cc: "glider@google.com" <glider@google.com>,
	"dvyukov@google.com" <dvyukov@google.com>,
	"jannh@google.com" <jannh@google.com>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"kasan-dev@googlegroups.com" <kasan-dev@googlegroups.com>,
	"hdanton@sina.com" <hdanton@sina.com>
Subject: RE: [PATCH v2 2/3] kfence: maximize allocation wait timeout duration
Date: Thu, 16 Sep 2021 15:45:16 +0000	[thread overview]
Message-ID: <858909f98f33478891056a840ad68b9f@AcuMS.aculab.com> (raw)
In-Reply-To: <abd74d5a-1236-4f0e-c123-a41e56e22391@huawei.com>

From: Kefeng Wang
> Sent: 16 September 2021 02:21
> 
> We found kfence_test will fails  on ARM64 with this patch with/without
> CONFIG_DETECT_HUNG_TASK,
> 
> Any thought ?
> 
...
> >>       /* 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);

It has replaced a wait_event_timeout() with a wait_event().

That probably isn't intended.
Although I'd expect their to be some test for the wait being
signalled or timing out.

	David

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