Re: [PATCH 1/2] xfs: trylock underlying buffer on dquot flush

Brian Foster
2020-03-27T16:46:51Z

On Fri, Mar 27, 2020 at 12:44:40PM -0400, Brian Foster wrote:
> On Fri, Mar 27, 2020 at 08:45:28AM -0700, Darrick J. Wong wrote:
> > On Thu, Mar 26, 2020 at 09:17:02AM -0400, Brian Foster wrote:
> > > A dquot flush currently blocks on the buffer lock for the underlying
> > > dquot buffer. In turn, this causes xfsaild to block rather than
> > > continue processing other items in the meantime. Update
> > > xfs_qm_dqflush() to trylock the buffer, similar to how inode buffers
> > > are handled, and return -EAGAIN if the lock fails. Fix up any
> > > callers that don't currently handle the error properly.
> > >
> > > Signed-off-by: Brian Foster <bfoster@redhat.com>
> >
> > Is xfs_qm_dquot_isolate returning LRU_RETRY an acceptable resolution (as
> > opposed to, say, LRU_SKIP) for xfs_qm_dqflush returning -EAGAIN?
> >
>
> Hmm.. this is reclaim so I suppose LRU_SKIP would be more appropriate
> than retry (along with more consistent with the other trylock failures
> in that function). Ok with something like the following?
>
> @@ -461,7 +461,11 @@ xfs_qm_dquot_isolate(
> spin_unlock(lru_lock);
>
> error = xfs_qm_dqflush(dqp, &bp);
> - if (error)
> + if (error == -EAGAIN) {
> + xfs_dqunlock(dqp);
> + spin_lock(lru_lock);
> + goto out_miss_busy;
> + } else if (error)
> goto out_unlock_dirty;

Then again, is it safe to skip from here once we've cycled the lru_lock?

Brian

>
> xfs_buf_delwri_queue(bp, &isol->buffers);
>
> Brian
>
> > --D
> >
> > > ---
> > > fs/xfs/xfs_dquot.c | 6 +++---
> > > fs/xfs/xfs_dquot_item.c | 3 ++-
> > > fs/xfs/xfs_qm.c | 14 +++++++++-----
> > > 3 files changed, 14 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
> > > index 711376ca269f..af2c8e5ceea0 100644
> > > --- a/fs/xfs/xfs_dquot.c
> > > +++ b/fs/xfs/xfs_dquot.c
> > > @@ -1105,8 +1105,8 @@ xfs_qm_dqflush(
> > > * Get the buffer containing the on-disk dquot
> > > */
> > > error = xfs_trans_read_buf(mp, NULL, mp->m_ddev_targp, dqp->q_blkno,
> > > - mp->m_quotainfo->qi_dqchunklen, 0, &bp,
> > > - &xfs_dquot_buf_ops);
> > > + mp->m_quotainfo->qi_dqchunklen, XBF_TRYLOCK,
> > > + &bp, &xfs_dquot_buf_ops);
> > > if (error)
> > > goto out_unlock;
> > >
> > > @@ -1177,7 +1177,7 @@ xfs_qm_dqflush(
> > >
> > > out_unlock:
> > > xfs_dqfunlock(dqp);
> > > - return -EIO;
> > > + return error;
> > > }
> > >
> > > /*
> > > diff --git a/fs/xfs/xfs_dquot_item.c b/fs/xfs/xfs_dquot_item.c
> > > index cf65e2e43c6e..baad1748d0d1 100644
> > > --- a/fs/xfs/xfs_dquot_item.c
> > > +++ b/fs/xfs/xfs_dquot_item.c
> > > @@ -189,7 +189,8 @@ xfs_qm_dquot_logitem_push(
> > > if (!xfs_buf_delwri_queue(bp, buffer_list))
> > > rval = XFS_ITEM_FLUSHING;
> > > xfs_buf_relse(bp);
> > > - }
> > > + } else if (error == -EAGAIN)
> > > + rval = XFS_ITEM_LOCKED;
> > >
> > > spin_lock(&lip->li_ailp->ail_lock);
> > > out_unlock:
> > > diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
> > > index de1d2c606c14..68c778d25c48 100644
> > > --- a/fs/xfs/xfs_qm.c
> > > +++ b/fs/xfs/xfs_qm.c
> > > @@ -121,12 +121,11 @@ xfs_qm_dqpurge(
> > > {
> > > struct xfs_mount *mp = dqp->q_mount;
> > > struct xfs_quotainfo *qi = mp->m_quotainfo;
> > > + int error = -EAGAIN;
> > >
> > > xfs_dqlock(dqp);
> > > - if ((dqp->dq_flags & XFS_DQ_FREEING) || dqp->q_nrefs != 0) {
> > > - xfs_dqunlock(dqp);
> > > - return -EAGAIN;
> > > - }
> > > + if ((dqp->dq_flags & XFS_DQ_FREEING) || dqp->q_nrefs != 0)
> > > + goto out_unlock;
> > >
> > > dqp->dq_flags |= XFS_DQ_FREEING;
> > >
> > > @@ -139,7 +138,6 @@ xfs_qm_dqpurge(
> > > */
> > > if (XFS_DQ_IS_DIRTY(dqp)) {
> > > struct xfs_buf *bp = NULL;
> > > - int error;
> > >
> > > /*
> > > * We don't care about getting disk errors here. We need
> > > @@ -149,6 +147,8 @@ xfs_qm_dqpurge(
> > > if (!error) {
> > > error = xfs_bwrite(bp);
> > > xfs_buf_relse(bp);
> > > + } else if (error == -EAGAIN) {
> > > + goto out_unlock;
> > > }
> > > xfs_dqflock(dqp);
> > > }
> > > @@ -174,6 +174,10 @@ xfs_qm_dqpurge(
> > >
> > > xfs_qm_dqdestroy(dqp);
> > > return 0;
> > > +
> > > +out_unlock:
> > > + xfs_dqunlock(dqp);
> > > + return error;
> > > }
> > >
> > > /*
> > > --
> > > 2.21.1
> > >
> >
>