lkml.org 
[lkml]   [2012]   [Jun]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/4] Was: deferring __fput()
On 06/30, Al Viro wrote:
>
> On Thu, Jun 28, 2012 at 06:45:39PM +0200, Oleg Nesterov wrote:
> > Forgot to mention...
> >
> > And I still think that task_work_add() should not succeed unconditionally,
> > it synchronize with exit_task_work(). Otherwise keyctl_session_to_parent()
> > is broken.
>
> Hmm... Look: if nothing else, we have
> /* the parent mustn't be init and mustn't be a kernel thread */
> if (parent->pid <= 1 || !parent->mm)
> goto unlock;
> in the caller. OTOH, on the exit side we have exit_mm() done first. And
> that will have ->mm set to NULL. So we are closing a very narrow race to start
> with. So why not do the following and be done with that?

Of course we can fix keyctl_session_to_parent(). But why? I mean, why
do you dislike the idea to put this synchronization into add/run ?

IMO, this makes task_work much less useful/convenient. Every caller
has to fight with this race somehow. And the lock it can take depends
on the context, say, you can't use task_lock() in irq.

IOW, what is wrong with

[PATCH 2/4] task_work: don't rely on PF_EXITING
http://marc.info/?l=linux-kernel&m=134082265321691

and
[PATCH 3/4] task_work: deal with task_work callbacks adding more work
http://marc.info/?t=134082275400004

?

perhaps you do not like the fact that the exiting task takes pi_lock
unconditionally?



and in fact I think that probably it makes sense to change fput,

- task_work_add(current, ...);
+ BUG_ON(task_work_add(current, ...) != 0);

Oleg.



\
 
 \ /
  Last update: 2012-06-30 20:21    [W:0.107 / U:0.192 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site