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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Alan Stern <stern@rowland.harvard.edu>
Subject: Re: [Bug 10030] Suspend doesn't work when SD card is inserted
Date: Mon, 25 Feb 2008 12:41:25 +0100
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Cc: Pavel Machek <pavel@ucw.cz>, Pierre Ossman <drzeus-mmc@drzeus.cx>,
       Zdenek Kabelac <zdenek.kabelac@gmail.com>,
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On Monday, 25 of February 2008, Alan Stern wrote:
> 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.

Yeah, I've already realized it was a stupid idea. :-)

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

So can you do that, pretty please?

Thanks,
Rafael