Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/1] futex: check PF_KTHREAD rather than !p->mm to filter out kthreads | From | Davidlohr Bueso <> | Date | Sat, 14 Feb 2015 10:01:06 -0800 |
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On Mon, 2015-02-02 at 15:05 +0100, Oleg Nesterov wrote: > attach_to_pi_owner() checks p->mm to prevent attaching to kthreads and > this looks doubly wrong: > > 1. It should actually check PF_KTHREAD, kthread can do use_mm(). > > 2. If this task is not kthread and it is actually the lock owner we can > wrongly return -EPERM instead of -ESRCH or retry-if-EAGAIN. > > And note that this wrong EPERM is the likely case unless the exiting > task is (auto)reaped quickly, we check ->mm before PF_EXITING. > > Signed-off-by: Oleg Nesterov <oleg@redhat.com> > --- > kernel/futex.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/kernel/futex.c b/kernel/futex.c > index 63678b5..b101381 100644 > --- 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, a quick search shows that, at least, the oom killer and proc have this same problem. 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; +} + /* __GFP_IO isn't allowed if PF_MEMALLOC_NOIO is set in current->flags * __GFP_FS is also cleared as it implies __GFP_IO. */
Thanks, Davidlohr
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