Re: [PATCH] f2fs: add memory barrier for wait list and pages count

[Jaegeuk Kim <jaegeuk@kernel.org>]

Hi Hong Mei,

In order to avoid this problem, we already added wq_has_sleeper() which calls
smp_mb() in end_io, and use io_schedule_timeout() instead of io_schedule() in
wait_on_all_pages_writeback().

How do you think whether this is enough or not?

Thanks,

On Wed, Mar 09, 2016 at 01:42:12PM -0800, Hong Mei Li wrote:
> From: Hong-Mei Li <a21834@motorola.com>
> 
> 
> Sometimes, f2fs fdatasync would stuck at wait_on_all_pages_writeback
> with pages count == 0 and itself in the waitlist.
> 
> Fix it by adding an explicit smp_mb() after writting wait list, to make
> sure the store is done before get_pages.
> And add another memory barrier in wakeup side, to make sure cpu reading
> wait list happens after decreased pages count syncing to memory.
> 
> Signed-off-by: Hong-Mei Li <a21834@motorola.com>
> Cc: linux-f2fs-devel@lists.sourceforge.net
> Cc: Jaegeuk Kim <jaegeuk@kernel.org>
> 
> ---
>  fs/f2fs/checkpoint.c | 1 +
>  fs/f2fs/data.c       | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index 3842af9..4e5acab 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -899,6 +899,7 @@ static void wait_on_all_pages_writeback(struct
> f2fs_sb_info *sbi)
>         for (;;) {
>                 prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
> 
> +               smp_mb();
>                 if (!get_pages(sbi, F2FS_WRITEBACK))
>                         break;
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 5c06db1..b1d383c 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -75,6 +75,7 @@ static void f2fs_write_end_io(struct bio *bio)
>                 dec_page_count(sbi, F2FS_WRITEBACK);
>         }
> 
> +       smp_mb();
>         if (!get_pages(sbi, F2FS_WRITEBACK) &&
>                         !list_empty(&sbi->cp_wait.task_list))
>                 wake_up(&sbi->cp_wait);
> -- 
> 1.9.1

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