Re: [PATCH] f2fs: avoid hungtask problem caused by losing wake_up

[He YunLei <heyunlei@huawei.com>]

On 2016/2/23 13:44, Chao Yu wrote:
> Hi Yunlei,
Hi Chao,
>
>> -----Original Message-----
>> From: Yunlei He [mailto:heyunlei@huawei.com]
>> Sent: Tuesday, February 23, 2016 12:08 PM
>> To: chao2.yu@samsung.com; jaegeuk@kernel.org; linux-f2fs-devel@lists.sourceforge.net
>> Cc: bintian.wang@huawei.com; Yunlei He; Biao He
>> Subject: [f2fs-dev] [PATCH] f2fs: avoid hungtask problem caused by losing wake_up
>>
>> The D state of wait_on_all_pages_writeback should be waken by
>> function f2fs_write_end_io when all writeback pages have been
>> succesfully written to device. It's possible that wake_up comes
>> between get_pages and io_schedule. Maybe in this case it will
>> lost wake_up and still in D state even if all pages have been
>> write back to device, and finally, the whole system will be into
>> the hungtask state.
>
> I haven't encountered such issue so far, do you suffer this in real
> world?
>
yes, I have encounter it, the whole file system is blocked at function
wait_on_all_pages_writeback beyond 120s when write cp, and no error reported
by storage device driver.
>>
>>                  if (!get_pages(sbi, F2FS_WRITEBACK))
>>                           break;
>> 					<---------  wake_up
>
> wake_up will put all tasks linked in sbi->cp_wait on run-queue, so
> here it should be save to call io_schedule, after being rescheduled,
> it will get the chance to check above condition to break out.
>
> Thanks,

Here, we just doubt something weird may cause wait_on_all_pages_writeback
could not be waken. Wake_up trigger only one time by last bio's end_io
function, if the thread happen to miss it, the thread will be in D state
forever. So we change the code to make wait_on_all_pages_writeback awaken
periodically, then check the condition.

>
>>                  io_schedule();
>>
>> Signed-off-by: Yunlei He <heyunlei@huawei.com>
>> Signed-off-by: Biao He <hebiao6@huawei.com>
>> ---
>>   fs/f2fs/checkpoint.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>> index 2bac8a1..f55355d 100644
>> --- a/fs/f2fs/checkpoint.c
>> +++ b/fs/f2fs/checkpoint.c
>> @@ -920,7 +920,7 @@ static void wait_on_all_pages_writeback(struct f2fs_sb_info *sbi)
>>   		if (!get_pages(sbi, F2FS_WRITEBACK))
>>   			break;
>>
>> -		io_schedule();
>> +		io_schedule_timeout(5*HZ);
>>   	}
>>   	finish_wait(&sbi->cp_wait, &wait);
>>   }
>> --
>> 1.9.1
>
>
>
> .
>


------------------------------------------------------------------------------
Site24x7 APM Insight: Get Deep Visibility into Application Performance
APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month
Monitor end-to-end web transactions and take corrective actions now
Troubleshoot faster and improve end-user experience. Signup Now!
http://pubads.g.doubleclick.net/gampad/clk?id=272487151&iu=/4140