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

[Chao Yu <chao2.yu@samsung.com>]

Hi Yunlei,

> -----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?

> 
>                 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,

>                 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



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