[Ocfs2-devel] [PATCH] ocfs2: Move orphan scan work to ocfs2_wq.

[Wengang Wang]

Sorry, I made a mistake.

The quotum worker is on the system work queue, so the ocfs2_truncate_log_worker
will not block it.

regards,
wengang.
On 10-05-28 17:12, Wengang Wang wrote:
> Hi Tao,
> 
> Checking the workers in ocfs2_wq, I found osb_truncate_log_wq. The worker
> function ocfs2_truncate_log_worker() can with the following call trace.
> 
> ocfs2_truncate_log_worker()
> ocfs2_flush_truncate_log()
> __ocfs2_flush_truncate_log()
> ocfs2_inode_lock()
> 
> So I think during ocfs2_inode_lock(), we still have the possibility that
> it hang the work queue at dlm_wait_for_node_death().
> 
> So maybe a dedicated work queue is the only choice?
> 
> regards,
> wengang.
> On 10-05-28 14:22, Tao Ma wrote:
> > We used to let orphan scan work in the default work queue,
> > but there is a corner case which will make the system deadlock.
> > The scenario is like this:
> > 1. set heartbeat threadshold to 200. this will allow us to have a
> >    great chance to have a orphan scan work before our quorum decision.
> > 2. mount node 1.
> > 3. after 1~2 minutes, mount node 2(in order to make the bug easier
> >    to reproduce, better add maxcpus=1 to kernel command line).
> > 4. node 1 do orphan scan work.
> > 5. node 2 do orphan scan work.
> > 6. node 1 do orphan scan work. After this, node 1 hold the orphan scan
> >    lock while node 2 know node 1 is the master.
> > 7. ifdown eth2 in node 2(eth2 is what we do ocfs2 interconnection).
> > 
> > Now when node 2 begins orphan scan, the system queue is blocked.
> > 
> > The root cause is that both orphan scan work and quorum decision work
> > will use the system event work queue. orphan scan has a chance of
> > blocking the event work queue(in dlm_wait_for_node_death) so that there
> > is no chance for quorum decision work to proceed.
> > 
> > This patch resolve it by moving orphan scan work to ocfs2_wq.
> > 
> > Signed-off-by: Tao Ma <tao.ma at oracle.com>
> > ---
> >  fs/ocfs2/journal.c |    6 +++---
> >  1 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c
> > index 57e3fef..e02788f 100644
> > --- a/fs/ocfs2/journal.c
> > +++ b/fs/ocfs2/journal.c
> > @@ -1938,7 +1938,7 @@ void ocfs2_orphan_scan_work(struct work_struct *work)
> >  	mutex_lock(&os->os_lock);
> >  	ocfs2_queue_orphan_scan(osb);
> >  	if (atomic_read(&os->os_state) == ORPHAN_SCAN_ACTIVE)
> > -		schedule_delayed_work(&os->os_orphan_scan_work,
> > +		queue_delayed_work(ocfs2_wq, &os->os_orphan_scan_work,
> >  				      ocfs2_orphan_scan_timeout());
> >  	mutex_unlock(&os->os_lock);
> >  }
> > @@ -1978,8 +1978,8 @@ void ocfs2_orphan_scan_start(struct ocfs2_super *osb)
> >  		atomic_set(&os->os_state, ORPHAN_SCAN_INACTIVE);
> >  	else {
> >  		atomic_set(&os->os_state, ORPHAN_SCAN_ACTIVE);
> > -		schedule_delayed_work(&os->os_orphan_scan_work,
> > -				      ocfs2_orphan_scan_timeout());
> > +		queue_delayed_work(ocfs2_wq, &os->os_orphan_scan_work,
> > +				   ocfs2_orphan_scan_timeout());
> >  	}
> >  }
> >  
> > -- 
> > 1.5.5
> > 
> > 
> > _______________________________________________
> > Ocfs2-devel mailing list
> > Ocfs2-devel at oss.oracle.com
> > http://oss.oracle.com/mailman/listinfo/ocfs2-devel
> 
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