linux-kernel - Re: Regression in suspend to ram in 2.6.31-rc kernels

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Message-Id: <200909142117.03726.rjw@sisk.pl>
Date:	Mon, 14 Sep 2009 21:17:03 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Zdenek Kabelac <zdenek.kabelac@...il.com>
Cc:	Chris Ball <cjb@...top.org>, Pavel Machek <pavel@....cz>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Christoph Hellwig <hch@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mmc@...r.kernel.org, viro@...iv.linux.org.uk
Subject: Re: Regression in suspend to ram in 2.6.31-rc kernels

On Monday 14 September 2009, Zdenek Kabelac wrote:
> 2009/9/12 Rafael J. Wysocki <rjw@...k.pl>:
> > On Saturday 12 September 2009, Chris Ball wrote:
> >> Hi,
> >>
> >>    > Well system could check basic card ids if they match after resume
> >>
> >> No.  That (arguably) guarantees that it's the same card, but not that
> >> it wasn't modified in another machine during the suspend.
> >
> > Generally speaking, we'd also need to check superblocks for this to work.
> >
> >>    > if some users wants to crash his card by randomly swapping it
> >>    > during suspend/resume - I'd have no problem with that....
> >>
> >> You should have a problem with it.  Taking a card from a suspended
> >> machine and working on it with a different machine is not a bizarre
> >> thing to want to do.
> >
> > Agreed.
> 
> 
> Well - ok - so let me ask this question - if I'll replace local hard
> drive during suspend - what will happen - is this prohibited by hw
> (e.i. to switch SATA cables) ?

That I'm unsure of, but if you replace some other major components, such
as the CPU or memory, the hardware will detect that and the resume will fail.

> IMHO filesystem should be able to detect corruption of its data
> structures - (assuming fs is notified about suspend/resume operation)

Well, the problem is that at the moment such a notification mechanism doesn't
exist.

> Also there could be one simple quick solution/hack

No hacks, please.

> - to require to have at least all remote drives unmounted - so suspend would

Define "remote".  It isn't that simple, even your root fs can be on USB, iSCSI,
whatever.

> be refused if it runs mounted card/usb drive -  this would be 100% better
> than current solution which effectively kills my laptop if I forget to
> unmount card in mmc reader - especially if dmesg contains message with
> the reason why my suspend fails.

You can make the suspend scripts check for that, there's no reason for the
kernel to do it IMO.

Thanks,
Rafael
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