В Вс, 21/09/2014 в 00:09 +0400, Kirill Tkhai пишет: > В Сб, 20/09/2014 в 20:54 +0200, Peter Zijlstra пишет: > > On Sat, Sep 20, 2014 at 08:33:26PM +0200, Peter Zijlstra wrote: > > > On Sat, Sep 20, 2014 at 08:51:22PM +0400, Kirill Tkhai wrote: > > > > From: Kirill Tkhai <[email protected]> > > > > > > > > We may pick a task which is in context_switch() on other cpu at the > > > > moment. > > > > Parallel using of a single stack by two processes is not a good idea. > > > > > > Please elaborate on who exactly that might happen. Its best to have > > > comprehensive changelogs for issues that fix races. > > > > FWIW IIRC we can remove UNLOCKED_CTXSW from IA64 and I forgot if I > > audited MIPS, but I suspect we can (and should) remove it there too. > > > > That would make this exception go away and clean up some of this ugly. > > Yeah, you've said me about IA64: > > http://www.spinics.net/lists/linux-ia64/msg10229.html > > It's about 10 years since the logic, which was documented in ia64 > header, has been removed. It looks like, ia64 maintainers are not > interested much... > > *** > > To do not to start a new message. I've found the above when I was > analysing if the optimisation below is OK (assume, we have accessor > cpu_relax__while_on_cpu()): > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 7d0d023..8d765ba 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1699,8 +1699,6 @@ try_to_wake_up(struct task_struct *p, unsigned int > state, int wake_flags) > goto stat; > > #ifdef CONFIG_SMP > - cpu_relax__while_on_cpu(p); > - > p->sched_contributes_to_load = !!task_contributes_to_load(p); > p->state = TASK_WAKING; > > @@ -1708,6 +1706,9 @@ try_to_wake_up(struct task_struct *p, unsigned int > state, int wake_flags) > p->sched_class->task_waking(p); > > cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags); > + > + cpu_relax__while_on_cpu(p); > + > if (task_cpu(p) != cpu) { > wake_flags |= WF_MIGRATED; > set_task_cpu(p, cpu); > > Looks like, now problem here. Task p is dequeued, we can set > sched_contributes_to_load and state
s/now/no/ > here, also task_waking does not produce problems, only arithmetics is there. > select_task_rq() > is R/O function. > > Now I'm testing this. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
