On Fri, Apr 21, 2017 at 08:22:12AM -0400, Brian Foster wrote:
> The quotacheck error handling of the delwri buffer list assumes the
> resident buffers are locked and doesn't clear the _XBF_DELWRI_Q flag
> on the buffers that are dequeued. This can lead to assert failures
> on buffer release and possibly other locking problems.
>
> Move this code to a delwri queue cancel helper function to
> encapsulate the logic required to properly release buffers from a
> delwri queue. Update the helper to clear the delwri queue flag and
> call it from quotacheck.
>
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
I /think/ this one is ok -- it's useful to assert that the buffer is
actually locked before we try to unlock it, and the other parts refactor
existing code.
If we want to be super-pedantic, then yes, delwri_submit consumes the
entire list and we don't need to touch buffer_list if we hit the final
"goto error_return;" in quotacheck. OTOH I feel like there's not much
harm in the extra list_empty check and should we ever decide that
delwri_submit shouldn't consume the whole list, then we're already
covered.
Regardless, if anyone /does/ want that change, it can be a separate
patch.
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> fs/xfs/xfs_buf.c | 24 ++++++++++++++++++++++++
> fs/xfs/xfs_buf.h | 1 +
> fs/xfs/xfs_qm.c | 7 +------
> 3 files changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index b620872..ba036c1 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1079,6 +1079,8 @@ void
> xfs_buf_unlock(
> struct xfs_buf *bp)
> {
> + ASSERT(xfs_buf_islocked(bp));
> +
> XB_CLEAR_OWNER(bp);
> up(&bp->b_sema);
>
> @@ -1815,6 +1817,28 @@ xfs_alloc_buftarg(
> }
>
> /*
> + * Cancel a delayed write list.
> + *
> + * Remove each buffer from the list, clear the delwri queue flag and drop the
> + * associated buffer reference.
> + */
> +void
> +xfs_buf_delwri_cancel(
> + struct list_head *list)
> +{
> + struct xfs_buf *bp;
> +
> + while (!list_empty(list)) {
> + bp = list_first_entry(list, struct xfs_buf, b_list);
> +
> + xfs_buf_lock(bp);
> + bp->b_flags &= ~_XBF_DELWRI_Q;
> + list_del_init(&bp->b_list);
> + xfs_buf_relse(bp);
> + }
> +}
> +
> +/*
> * Add a buffer to the delayed write list.
> *
> * This queues a buffer for writeout if it hasn't already been. Note that
> diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
> index e1bc1af..8d1d44f 100644
> --- a/fs/xfs/xfs_buf.h
> +++ b/fs/xfs/xfs_buf.h
> @@ -329,6 +329,7 @@ extern void *xfs_buf_offset(struct xfs_buf *, size_t);
> extern void xfs_buf_stale(struct xfs_buf *bp);
>
> /* Delayed Write Buffer Routines */
> +extern void xfs_buf_delwri_cancel(struct list_head *);
> extern bool xfs_buf_delwri_queue(struct xfs_buf *, struct list_head *);
> extern int xfs_buf_delwri_submit(struct list_head *);
> extern int xfs_buf_delwri_submit_nowait(struct list_head *);
> diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
> index b669b12..8b9a9f1 100644
> --- a/fs/xfs/xfs_qm.c
> +++ b/fs/xfs/xfs_qm.c
> @@ -1384,12 +1384,7 @@ xfs_qm_quotacheck(
> mp->m_qflags |= flags;
>
> error_return:
> - while (!list_empty(&buffer_list)) {
> - struct xfs_buf *bp =
> - list_first_entry(&buffer_list, struct xfs_buf, b_list);
> - list_del_init(&bp->b_list);
> - xfs_buf_relse(bp);
> - }
> + xfs_buf_delwri_cancel(&buffer_list);
>
> if (error) {
> xfs_warn(mp,
> --
> 2.7.4
>
> --
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