Messages in this thread | | | Subject | Re: [PATCH] account_group_exec_runtime: fix the racy usage of ->signal | From | Peter Zijlstra <> | Date | Mon, 10 Nov 2008 13:13:26 +0100 |
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On Mon, 2008-11-10 at 14:04 +0100, Oleg Nesterov wrote: > On 11/08, Ingo Molnar wrote: > > > > * Oleg Nesterov <oleg@redhat.com> wrote: > > > > > On 11/07, Ingo Molnar wrote: > > > > > > > > the signal lock must not nest inside the rq > > > > lock, and these accounting functions are called from within the > > > > scheduler. > > > > > > Why? we seem to never do task_rq_lock() under ->siglock ? > > > > signal_wake_up() ? > > I'd wish very much I could say I have already realized this, but I didn't. > Thanks Ingo! > > I don't see the good solution for this problem. I'll send the new patch in > a minute, but it is ugly. Basically it is > > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -141,6 +141,8 @@ static void __exit_signal(struct task_st > if (sig) { > flush_sigqueue(&sig->shared_pending); > taskstats_tgid_free(sig); > + smp_mb(); > + spin_unlock_wait(&task_rq(tsk)->lock); > __cleanup_signal(sig); > } > } > > except this needs a helper in sched.c. You can nack it right now ;) > Of course we can protect ->signal with rcu, but this is even worse > imho. > > Anybody sees a bettter fix? > > > Perhaps we can change sched.c to do update_curr() only when the > task is not running (except ->task_tick), iow perhaps we can check > sleep/wakeup == T before calling update_cur(). But this is not easy > even if really possible.
and butt ugly to boot..
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