2017-10-29 23:10 GMT+09:00 Andreas Rohner <andreas.rohner@xxxxxxx>:
> 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@xxxxxxx>
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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