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From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Tejun Heo <htejun@gmail.com>
Cc: Mark Lord <liml@rtr.ca>, Matthew Wilcox <matthew@wil.cx>,
	linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org,
	Jeff Garzik <jeff@garzik.org>
Subject: Re: ata_ram driver
Date: Thu, 06 Mar 2008 18:01:59 -0600	[thread overview]
Message-ID: <1204848119.3062.94.camel@localhost.localdomain> (raw)
In-Reply-To: <47D08478.8010700@gmail.com>

On Fri, 2008-03-07 at 08:55 +0900, Tejun Heo wrote:
> James Bottomley wrote:
> >> It's because of the sequence of events.  Currently, driver unload
> >> sequence is the same as when the device is hot unplugged.  libata
> >> detects that the device is gone and disables it and report it to SCSI
> >> layer.  SCSI layer takes over and tries to kill the SCSI device and tell
> >> sd to shutdown and sd issues START_STOP to shutdown which fails w/
> >> DID_BAD_TARGET because the matching ATA device is already gone.  I've
> >> left it that way because I'm not sure whether spinning down the drive on
> >> driver unload is the correct thing to do.  The message is annoying tho.
> > 
> > Um, it's not supposed to happen that way.  Your signal that a disk is
> > gone is slave destroy ... and we don't call that until after the target
> > has been processed.  Devices are supposed to stay online (if possible)
> > from slave alloc to slave destroy.
> 
> Currently, it's like the following.
> 
> * Explicit unplug request via sysfs or whatever: ATA device stays online
> till slave_destroy finishes.

That's correct

> * Hot unplugging: Nothing much libata can do.  ATA device is yanked out
> by the user.

Yes, us too ... you just have to error all commands when the device
vanishes.

> * Driver unload: Dealt the same way as hot unplugging.

This is the problem case: driver unloading should have a
scsi_remove_host() in its path.  This is the trigger that sends out the
flushes/stops and calls slave_destroy.  scsi_remove_host() doesn't
actually return until all the destroys are completed, so it makes module
unloading wait until everything is properly shut down.

> Making driver unload like explicit unplug request is possible but it
> will mean that drives will be spun down on driver unload, which can be
> annoying to developers. 

You have a sysfs flag to prevent that, don't you?

>  In addition, the code path is shared with
> controller hot unplug in which case it's probably best not to issue any
> new command.  So, I've been reluctant to make the change.  If the change
> is required, I think it can be done by adding a few lines at the top of
> ata_port_detach().  Jeff, what do you think?

James



  reply	other threads:[~2008-03-07  0:02 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-22 20:09 Matthew Wilcox
2008-02-22 21:27 ` Mark Lord
2008-03-06  8:21   ` Tejun Heo
2008-03-06 15:28     ` James Bottomley
2008-03-06 23:55       ` Tejun Heo
2008-03-07  0:01         ` James Bottomley [this message]
2008-03-07  0:13           ` Tejun Heo
2008-03-07  0:22             ` James Bottomley
2008-03-07  0:28               ` Tejun Heo
2008-03-07  0:39                 ` James Bottomley
2008-03-07  0:43                   ` Tejun Heo
2008-03-07  3:08                     ` [PATCH 1/2] scsi: export scsi_forget_host() Tejun Heo
2008-03-07  3:11                       ` [PATCH 2/2] libata: kill SCSI devices before detaching ata_host Tejun Heo
2008-03-07  2:16                 ` ata_ram driver Jeff Garzik
2008-03-07  2:44                   ` James Bottomley

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