linux-kernel - Re: sata_mv port lockup on hotplug (kernel 2.6.38.2)

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Message-ID: <20110906164221.GH18425@mtj.dyndns.org>
Date:	Wed, 7 Sep 2011 01:42:21 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Bruce Stenning <b.stenning@...igovision.com>
Cc:	Mark Lord <kernel@...savvy.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	Jeff Garzik <jgarzik@...ox.com>
Subject: Re: sata_mv port lockup on hotplug (kernel 2.6.38.2)

On Wed, Sep 07, 2011 at 01:33:55AM +0900, Tejun Heo wrote:
> Hello,
> 
> On Tue, Sep 06, 2011 at 01:19:44PM +0100, Bruce Stenning wrote:
> > ata4: EH complete
> > Waking error handler thread
> > scsi_eh_wakeup: succeeded
> > scsi_schedule_eh: succeeded
> > scsi_restart_operations: waking up host to restart
> > Error handler scsi_eh_3 sleeping
> 
> I think the following should fix the problem.  The code there is from
> the time when libata shared scsi_host->host_lock.  libata no longer
> does that so, in the current state, host_eh_scheduled can be cleared
> with actual pending EH condition.

Hmmm... maybe not.  Such race condition exists iff host_eh_scheduled
is incremented outside of ap->lock, which I can't see how.  Weird.
Can you please instrument the followings?

* print the caller of scsi_eh_wakeup().  "%pF" w/ (void *)_RET_IP_
  should do it.

* print why scsi_eh is going back to sleep immediately.
  ie. shost->host_failed, host_eh_scheduled, host_busy in
  scsi_error_handler().  It would also be nice to add some printks
  around schedule() and enable PRINTK_TIME.

Thanks.

-- 
tejun
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