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Subject: Re: [PATCH v2 2/3] kfence: maximize allocation wait timeout duration
From:   Kefeng Wang <wangkefeng.wang@huawei.com>
To:     Marco Elver <elver@google.com>, <akpm@linux-foundation.org>
CC:     <glider@google.com>, <dvyukov@google.com>, <jannh@google.com>,
        <mark.rutland@arm.com>, <linux-kernel@vger.kernel.org>,
        <linux-mm@kvack.org>, <kasan-dev@googlegroups.com>,
        <hdanton@sina.com>
References: <20210421105132.3965998-1-elver@google.com>
 <20210421105132.3965998-3-elver@google.com>
 <6c0d5f40-5067-3a59-65fa-6977b6f70219@huawei.com>
Message-ID: <abd74d5a-1236-4f0e-c123-a41e56e22391@huawei.com>
Date:   Thu, 16 Sep 2021 09:20:49 +0800
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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@mail.gmail.com
>>
>> Fix it by computing the timeout duration in terms of the current
>> sysctl_hung_task_timeout_secs value.
>>
>> Signed-off-by: Marco Elver <elver@google.com>
>> ---
>>   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);