Re: [PATCH] nilfs-utils: Fix conflicting data buffer error

[Ryusuke Konishi <konishi.ryusuke-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

2017-10-29 23:10 GMT+09:00 Andreas Rohner <andreas.rohner-hi6Y0CQ0nG0@public.gmane.org>:
> Under certain high concurrency loads, NILFS2 can produce a segment that
> crashes the cleanerd process with a conflicting data buffer error. The
> segment is perfectly valid and the file system is not corrupted.
> However, the cleanerd process can no longer be started and the file
> system will eventually fill up and cannot be used any more.
>
> The reason for this crash is, that a single logical segment can contain
> multiple partial segments. If a block is written in one partial segment
> and then immediately overwritten in another partial segment, then these
> blocks have the same inode number, checkpoint number and offset.
> However, these three numbers are used by the kernel to uniquely
> identify a block. If the cleaner tries to clean two blocks that point
> to the exact same buffer_head in the kernel, it creates a conflicting
> data buffer error.
>
> The solution is to detect these blocks and treat them as dead blocks.
> If vd_period.p_end is equal to the checkpoint number, it means that the
> block was overwritten within the same logical segment. So it must be
> dead, and there is another block with the same ino, cno, and offset,
> which is alive.
>
> Signed-off-by: Andreas Rohner <andreas.rohner-hi6Y0CQ0nG0@public.gmane.org>

Applied.  Thank you!

Ryusuke Konishi

> ---
>  lib/gc.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/lib/gc.c b/lib/gc.c
> index 5e14443..9449352 100644
> --- a/lib/gc.c
> +++ b/lib/gc.c
> @@ -433,6 +433,19 @@ static int nilfs_vdesc_is_live(const struct nilfs_vdesc *vdesc,
>                 return vdesc->vd_period.p_end == NILFS_CNO_MAX;
>         }
>
> +       if (vdesc->vd_period.p_end == vdesc->vd_cno) {
> +               /*
> +                * This block was overwritten in the same logical segment, but
> +                * in a different partial segment. Probably because of
> +                * fdatasync() or a flush to disk.
> +                * Without this check, gc will cause buffer confliction error
> +                * if both partial segments are cleaned at the same time.
> +                * In that case there will be two vdesc with the same ino,
> +                * cno and offset.
> +                */
> +               return 0;
> +       }
> +
>         if (vdesc->vd_period.p_end == NILFS_CNO_MAX ||
>             vdesc->vd_period.p_end > protect)
>                 return 1;
> --
> 2.14.3
>
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