linux-kernel - Re: [linux-pm] Is it supposed to be ok to call del

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Date:	Fri, 04 Jun 2010 14:20:16 +0300
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Jens Axboe <jens.axboe@...cle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	linux-pm <linux-pm@...ts.linux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [linux-pm] Is it supposed to be ok to call del_gendisk while
 userspace is frozen?

On Thu, 2010-03-04 at 14:53 +0100, Pavel Machek wrote: 
> Hi!
> 
> > > journalling assumptions broken: commit block is there, but previous
> > > blocks are not intact. Data loss.
> > > 
> > > ...and that was the first I could think about. Lets not do
> > >  this. Barriers were invented for a reason.
> > 
> > Very well.  Then we still need a solution to the original problem:  
> > Devices sometimes need to be unregistered during resume, but
> > del_gendisk() blocks on the writeback thread, which is frozen until
> > after the resume finishes.  How do you suggest this be fixed?
> 
> Avoid unregistering device during resume. Instead, return errors until
> resume is done and you can call del_gendisk? 

This won't help ether. The same driver needs to unregister perfectly
working device on suspend, because the user might replace the card
during suspend and fool the os.
There is a setting, CONFIG_MMC_UNSAFE_RESUME and I use it, but it isn't
default.

Anyway to revive that old thread, how about introducing new
del_gendisk_no_sync?

A less safe version of del_gendisk, but which won't sync the filesystem.
Since driver knows that card is gone, there is no point of syncing it.

(the sync is done by invalidate_partition, so some flag should be
propagated to it).



Best regards,
Maxim Levitsky

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