Re: [PATCH 1/7] Freezer: Read PF_BORROWED_MM in a nonracy way

[Gautham R Shenoy <ego@in.ibm.com>]

On Sat, May 12, 2007 at 12:41:54PM +0200, Rafael J. Wysocki wrote:
> 
> Still, the following scenario is possible while we're freezing users space
> tasks:
> 
> (1) user space task calls daemonize()
> (2) freezer checks if this is a user space task and the test returns 'true'
> (3) task calls exit_mm() and clears its TIF_FREEZE
> (4) freezer sets TIF_FREEZE for the task
> (5) task calls try_to_freeze() and freezes itself (bad!)
> 
> To prevent this from happening, I think, we should acquire task_lock() around
> the entire block in which the test is made and TIF_FREEZE is set for the task,
> so something more sophisticated than
> freezer-read-pf_borrowed_mm-in-a-nonracy-way.patch is needed.
>

Hmmm, turns out Linus was right, after all! The caller needs to acquire
the task_lock().

> Well, I think we should ask Andrew to drop this patch and try to address the
> issue in the next series of patches.

I think it's a good idea. 

I would want to review the patches again. The more I look at them,
the better I seem to understand the subtleties in the freezer code.

> 
> Greetings,
> Rafael

Thanks and Regards
gautham.
-- 
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"