From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp2130.oracle.com ([141.146.126.79]:50206 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391345AbfFKQGt (ORCPT ); Tue, 11 Jun 2019 12:06:49 -0400 Date: Tue, 11 Jun 2019 09:06:27 -0700 From: "Darrick J. Wong" Subject: Re: [PATCH 09/10] xfs: poll waiting for quotacheck Message-ID: <20190611160627.GS1871505@magnolia> References: <155968496814.1657646.13743491598480818627.stgit@magnolia> <155968502703.1657646.17911228005649046316.stgit@magnolia> <20190611150712.GB10942@bfoster> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190611150712.GB10942@bfoster> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Brian Foster Cc: linux-xfs@vger.kernel.org On Tue, Jun 11, 2019 at 11:07:12AM -0400, Brian Foster wrote: > On Tue, Jun 04, 2019 at 02:50:27PM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong > > > > Create a pwork destroy function that uses polling instead of > > uninterruptible sleep to wait for work items to finish so that we can > > touch the softlockup watchdog. IOWs, gross hack. > > > > Signed-off-by: Darrick J. Wong > > --- > > Seems reasonable given the quirky circumstances of quotacheck. Just a > couple nits.. > > > fs/xfs/xfs_iwalk.c | 3 +++ > > fs/xfs/xfs_iwalk.h | 3 ++- > > fs/xfs/xfs_pwork.c | 21 +++++++++++++++++++++ > > fs/xfs/xfs_pwork.h | 2 ++ > > fs/xfs/xfs_qm.c | 2 +- > > 5 files changed, 29 insertions(+), 2 deletions(-) > > > > > > diff --git a/fs/xfs/xfs_iwalk.c b/fs/xfs/xfs_iwalk.c > > index 71ee1628aa70..c4a9c4c246b7 100644 > > --- a/fs/xfs/xfs_iwalk.c > > +++ b/fs/xfs/xfs_iwalk.c > > @@ -526,6 +526,7 @@ xfs_iwalk_threaded( > > xfs_ino_t startino, > > xfs_iwalk_fn iwalk_fn, > > unsigned int max_prefetch, > > + bool polled, > > void *data) > > { > > struct xfs_pwork_ctl pctl; > > @@ -556,5 +557,7 @@ xfs_iwalk_threaded( > > startino = XFS_AGINO_TO_INO(mp, agno + 1, 0); > > } > > > > + if (polled) > > + return xfs_pwork_destroy_poll(&pctl); > > return xfs_pwork_destroy(&pctl); > > Rather than have duplicate destruction paths, could we rework > xfs_pwork_destroy_poll() to something like xfs_pwork_poll() that just > does the polling and returns, then the caller can fall back into the > current xfs_pwork_destroy()? I.e., this ends up looking like: > > ... > /* poll to keep soft lockup watchdog quiet */ > if (polled) > xfs_pwork_poll(&pctl); > return xfs_pwork_destroy(&pctl); Sounds good, will do! > > } > ... > > diff --git a/fs/xfs/xfs_pwork.c b/fs/xfs/xfs_pwork.c > > index 19605a3a2482..3b885e0b52ac 100644 > > --- a/fs/xfs/xfs_pwork.c > > +++ b/fs/xfs/xfs_pwork.c > ... > > @@ -97,6 +101,23 @@ xfs_pwork_destroy( > > return pctl->error; > > } > > > > +/* > > + * Wait for the work to finish and tear down the control structure. > > + * Continually poll completion status and touch the soft lockup watchdog. > > + * This is for things like mount that hold locks. > > + */ > > +int > > +xfs_pwork_destroy_poll( > > + struct xfs_pwork_ctl *pctl) > > +{ > > + while (atomic_read(&pctl->nr_work) > 0) { > > + msleep(1); > > + touch_softlockup_watchdog(); > > + } > > Any idea what the typical watchdog timeout is? Usually 30s for the hangcheck timeout. > I'm curious where the 1ms > comes from and whether we could get away with anything larger. I realize > that might introduce mount latency with the current sleep based > implementation, but we could also consider a waitqueue and using > something like wait_event_timeout() to schedule out for longer time > periods and still wake up immediately when the count drops to 0. That's a much better approach than this naïve one which waits unnecessarily after the pwork finishes; I'll replace it with this. The kernel doesn't export the hang check timeout variable, so I think I'll just set it to 1s, which should be infrequent enough not to use a lot of CPU and frequent enough that we don't spew warnings everywhere. --D > Brian > > > + > > + return xfs_pwork_destroy(pctl); > > +} > > + > > /* > > * Return the amount of parallelism that the data device can handle, or 0 for > > * no limit. > > diff --git a/fs/xfs/xfs_pwork.h b/fs/xfs/xfs_pwork.h > > index e0c1354a2d8c..08da723a8dc9 100644 > > --- a/fs/xfs/xfs_pwork.h > > +++ b/fs/xfs/xfs_pwork.h > > @@ -18,6 +18,7 @@ struct xfs_pwork_ctl { > > struct workqueue_struct *wq; > > struct xfs_mount *mp; > > xfs_pwork_work_fn work_fn; > > + atomic_t nr_work; > > int error; > > }; > > > > @@ -45,6 +46,7 @@ int xfs_pwork_init(struct xfs_mount *mp, struct xfs_pwork_ctl *pctl, > > unsigned int nr_threads); > > void xfs_pwork_queue(struct xfs_pwork_ctl *pctl, struct xfs_pwork *pwork); > > int xfs_pwork_destroy(struct xfs_pwork_ctl *pctl); > > +int xfs_pwork_destroy_poll(struct xfs_pwork_ctl *pctl); > > unsigned int xfs_pwork_guess_datadev_parallelism(struct xfs_mount *mp); > > > > #endif /* __XFS_PWORK_H__ */ > > diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c > > index e4f3785f7a64..de6a623ada02 100644 > > --- a/fs/xfs/xfs_qm.c > > +++ b/fs/xfs/xfs_qm.c > > @@ -1305,7 +1305,7 @@ xfs_qm_quotacheck( > > flags |= XFS_PQUOTA_CHKD; > > } > > > > - error = xfs_iwalk_threaded(mp, 0, xfs_qm_dqusage_adjust, 0, NULL); > > + error = xfs_iwalk_threaded(mp, 0, xfs_qm_dqusage_adjust, 0, true, NULL); > > if (error) > > goto error_return; > > > >