Messages in this thread |  | | Date | Sat, 14 Feb 2015 21:57:45 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/1] futex: check PF_KTHREAD rather than !p->mm to filter out kthreads |
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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.
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