linux-kernel - Re: [RESEND][PATCH-2.6.24-rc8] Fix fakephp deadlock

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Message-ID: <4797899E.6020207@mev.co.uk>
Date:	Wed, 23 Jan 2008 18:38:22 +0000
From:	Ian Abbott <abbotti@....co.uk>
To:	Greg KH <greg@...ah.com>
Cc:	linux-kernel@...r.kernel.org, linux-pci@...ey.karlin.mff.cuni.cz,
	pcihpd-discuss@...ts.sourceforge.net, gregkh@...e.de,
	kristen.c.accardi@...el.com
Subject: Re: [RESEND][PATCH-2.6.24-rc8] Fix fakephp deadlock

On 23/01/08 17:46, Greg KH wrote:
> On Tue, Jan 22, 2008 at 02:28:08PM +0000, Ian Abbott wrote:
>> #include <linux/init.h>
>> #include <linux/string.h>
>> #include <linux/slab.h>
>> +#include <linux/workqueue.h>
>> #include "../pci.h"
>> #if !defined(MODULE)
>> @@ -63,10 +64,13 @@ struct dummy_slot {
>> 	struct list_head node;
>> 	struct hotplug_slot *slot;
>> 	struct pci_dev *dev;
>> +	struct work_struct remove_work;
>> +	unsigned long removed;
> 
> You are treating "removed" as an atomic value, so why not just make it
> an atomic_t?

Because I'm using it as a boolean?

> And what is protecting the fact that the flag could be set right after
> it gets checked?  I don't see a lock here :)

Okay, it looks like there might be a race condition between 
enable_slot() and disable_slot() if some other task calls disable_slot() 
while enable_slot() is between the test_bit() and flush_workqueue() 
calls.  I can fix that by avoiding the call to flush_workqueue() in 
enable_slot() and allocating and queueing a work queue item to defer the 
call to pci_rescan().  And enable_slot() won't then need to check if the 
slot was marked as removed - it can just go ahead and allocate and queue 
a work item.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk>        )=-
-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-
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