linux-kernel - Re: Bug in SCSI async probing

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Message-ID: <Pine.LNX.4.44L0.0905261658430.11998-100000@iolanthe.rowland.org>
Date:	Tue, 26 May 2009 17:04:48 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	SCSI development list <linux-scsi@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Bug in SCSI async probing

On Tue, 26 May 2009, James Bottomley wrote:

> > > > (Which reminds me...  Are the calls in wait_scan_init() really enough?  
> > > > wait_for_device_probe() does async_synchronize_full() and then
> > > > scsi_complete_async_scans() finishes the SCSI scanning.  But if this
> > > > scanning involves calling sd_probe(), then more async work will be
> > > > queued.  Maybe a second call to wait_for_device_probe() is needed.)
> > 
> > You didn't respond to this point.
> 
> Well this was the response:
> 
> > > None of this really got reviewed through the SCSI list, so I'll let
> > > Arjan answer.

Whoops, for some reason I had gotten the idea that you wrote 
wait_scan_init().

> > Well then, how does this patch look?
> 
> Well, it's adding complexity, the best fix is to let async only take
> care of the pieces which can't fail, that way we don't need complex
> error handling.  The piece that slows probing isn't really the sysfs
> appearances, it's the SCSI probing, and the last piece that needs error
> handling is the device_add() for sysfs visibility, so that should be the
> dividing line between sync and async.

I had exactly the same thought, but it seemed less intrusive to keep
the dividing line where Arjan put it.

> This should restore the logical flow and fix all the error leg problems
> (by eliminating the error legs).

You forgot to move the dev_set_drvdata() call into the synchronous 
part.  Apart from that it looks fine.  Should I submit it officially?

Also, I do still think that wait_scan_init() needs an extra call to 
async_synchronize_full() at the end.

Alan Stern

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