linux-kernel - Re: [Bug 10030] Suspend doesn't work when SD card is inserted

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Date:	Sun, 24 Feb 2008 21:21:50 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Pavel Machek <pavel@....cz>, Pierre Ossman <drzeus-mmc@...eus.cx>,
	Zdenek Kabelac <zdenek.kabelac@...il.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [Bug 10030] Suspend doesn't work when SD card is inserted

On Sun, 24 Feb 2008, Rafael J. Wysocki wrote:

> > Very subtly wrong ;-).
> > 
> > imagine suspending_task == 0xabcdef01. Now task "R" with current ==
> > 0xabcd0000 reads suspending_task while the other cpu is writing to it,
> > and sees 0xabcd0000 (0xef01 was not yet written) -- and mistakenly
> > believes that  "R" == suspending_task.
> > 
> > I agree it is very unlikely, and it will not happen on i386. But what
> > about just using atomic_t suspending_task, and store current->pid into
> > it?
> 
> I'd rather use a lock, frankly.  For example, we can require the readers to
> take pm_sleep_rwsem for reading in order to access that.

That certainly won't work.  Imagine what would happen when the reader 
_was_ the suspending task.

But if you really twist my arm, I'll go along with Pavel's suggestion.

Alan Stern

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