lkml.org 
[lkml]   [2015]   [Feb]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/1] futex: check PF_KTHREAD rather than !p->mm to filter out kthreads
On 02/14, Davidlohr Bueso wrote:
>
> On Mon, 2015-02-02 at 15:05 +0100, Oleg Nesterov wrote:
> > --- a/kernel/futex.c
> > +++ b/kernel/futex.c
> > @@ -900,7 +900,7 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key,
> > if (!p)
> > return -ESRCH;
> >
> > - if (!p->mm) {
> > + if (unlikely(p->flags & PF_KTHREAD)) {
> > put_task_struct(p);
> > return -EPERM;
> > }
>
> Futexes aren't the only naughty checkers,

Yes, this is the common mistake,

> a quick search shows that, at
> least, the oom killer and proc have this same problem.

oom looks fine, note the PF_KTHREAD check in oom_unkillable(). It check ->mm
for another reason, to figure out if this task has passed exit_mm() or not.

proc looks fine too at first glance... we do not care if this mm was adopted
via use_mm() or not.

> Should we make
> this generic and update accordingly? ie:
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 8db31ef..b0d37d6 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1991,6 +1991,11 @@ extern void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut,
> #define tsk_used_math(p) ((p)->flags & PF_USED_MATH)
> #define used_math() tsk_used_math(current)
>
> +static inline bool task_is_kthread(struct task_struct *task)
> +{
> + return task->flags & PF_KTHREAD;
> +}

Perhaps... but PF_KTHREAD looks self-documented too ;)

Oleg.



\
 
 \ /
  Last update: 2015-02-14 22:21    [W:0.051 / U:1.792 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site