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

Brian Foster
2020-03-27T16:44:51Z

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;

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
> >
>