| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CAGWkznGk07jkuA8rftR0f5upq-7B6tkybSb_DMJYau0HjhYUnQ@mail.gmail.com>
Date: Tue, 21 Dec 2021 10:51:01 +0800
From: Zhaoyang Huang <huangzhaoyang@...il.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Johannes Weiner <hannes@...xchg.org>,
Zhaoyang Huang <zhaoyang.huang@...soc.com>,
"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] psi: fix possible trigger missing in the window
On Tue, Dec 21, 2021 at 10:30 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> On Mon, Dec 20, 2021 at 5:57 PM Zhaoyang Huang <huangzhaoyang@...il.com> wrote:
> >
> > On Tue, Dec 21, 2021 at 3:58 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
> > >
> > > On Fri, Dec 17, 2021 at 10:03 PM Zhaoyang Huang <huangzhaoyang@...il.com> wrote:
> > > >
> > > > loop Suren
> > >
> > > Thanks.
> > >
> > >
> > > >
> > > > On Fri, Dec 17, 2021 at 2:08 PM Huangzhaoyang <huangzhaoyang@...il.com> wrote:
> > > > >
> > > > > From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > > > >
> > > > > There could be missing wake up if the rest of the window remain the
> > > > > same stall states as the polling_total updates for every polling_min_period.
> > >
> > > Could you please expand on this description? I'm unclear what the
> > > problem is. I assume "polling_min_period" in this description refers
> > > to the group->poll_min_period.
> > >
> > > From the code, looks like the change results in update_triggers()
> > > calling window_update() once there was a new stall recorded for the
> > > trigger state and until the tracking window is complete. I don't see
> > > the point of calling window_update() if there was no stall change
> > > since the last call to window_update(). The resulting growth will not
> > > increase if there is no new stall.
> > > Maybe what you want to achieve here is more than one trigger per
> > > window if the stall limit was breached? If so, then this goes against
> > > the design for psi triggers in which we want to rate-limit the number
> > > of generated triggers per tracking window (see:
> > > https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L545).
> > > Please clarify the issue and the intentions here.
> > > Thanks!
> > Please correct me if I am wrong. Imagine that there is a new stall
> > during the 1st polling_min_period among 10 of them in the window and
> > group->polling_total will be updated to total without trigger. If the
> > rest of 9 polling_min_periods remain the same states, the trigger will
> > be missed when window timing is reached.
>
> I don't see why updating group->polling_total after the first
> registered stall is an issue here. window_update() calculates growth
> using current group->total[] and win->start_value (see:
> https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L483)
> which is set at the beginning of the window (see:
> https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L462).
> If the calculated growth did not reach t->threshold then the trigger
> should not be fired (see:
> https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L542).
> We fire the trigger only if growth within a given window is higher
> than the threshold.
>
> In your scenario if the stall recorded in the 1st polling_min_period
> was less than the threshold and in the other 9 polling_min_periods no
> new stalls were registered then there should be no triggers fired in
> that window. This is intended behavior. Trigger is fired only when the
The stall in the 1st polling_min_period was *LARGE* then the threshold
will also be ignored here.
> recorded stall within the window breaches the threshold. And there
> will be only one trigger generated per window, no matter how much
> stall is being recorded after the threshold was breached.
> Hopefully this clarifies the behavior?
I don't think so. According to your opinion, if the total keeps no
change in the last polling_min_period, then the growth during the 1-9
min_periods which is much larger than the threshold will also be
ignored. It does not make sense.
https://elixir.bootlin.com/linux/latest/source/kernel/sched/psi.c#L529
>
> > >
> > > > >
> > > > > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > > > > ---
> > > > > include/linux/psi_types.h | 2 ++
> > > > > kernel/sched/psi.c | 30 ++++++++++++++++++------------
> > > > > 2 files changed, 20 insertions(+), 12 deletions(-)
> > > > >
> > > > > diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
> > > > > index 0a23300..9533d2e 100644
> > > > > --- a/include/linux/psi_types.h
> > > > > +++ b/include/linux/psi_types.h
> > > > > @@ -132,6 +132,8 @@ struct psi_trigger {
> > > > >
> > > > > /* Refcounting to prevent premature destruction */
> > > > > struct kref refcount;
> > > > > +
> > > > > + bool new_stall;
> > > > > };
> > > > >
> > > > > struct psi_group {
> > > > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> > > > > index 1652f2b..402718c 100644
> > > > > --- a/kernel/sched/psi.c
> > > > > +++ b/kernel/sched/psi.c
> > > > > @@ -458,9 +458,12 @@ static void psi_avgs_work(struct work_struct *work)
> > > > > static void window_reset(struct psi_window *win, u64 now, u64 value,
> > > > > u64 prev_growth)
> > > > > {
> > > > > + struct psi_trigger *t = container_of(win, struct psi_trigger, win);
> > > > > +
> > > > > win->start_time = now;
> > > > > win->start_value = value;
> > > > > win->prev_growth = prev_growth;
> > > > > + t->new_stall = false;
> > > > > }
> > > > >
> > > > > /*
> > > > > @@ -515,7 +518,6 @@ static void init_triggers(struct psi_group *group, u64 now)
> > > > > static u64 update_triggers(struct psi_group *group, u64 now)
> > > > > {
> > > > > struct psi_trigger *t;
> > > > > - bool new_stall = false;
> > > > > u64 *total = group->total[PSI_POLL];
> > > > >
> > > > > /*
> > > > > @@ -523,19 +525,26 @@ static u64 update_triggers(struct psi_group *group, u64 now)
> > > > > * watchers know when their specified thresholds are exceeded.
> > > > > */
> > > > > list_for_each_entry(t, &group->triggers, node) {
> > > > > - u64 growth;
> > > > > -
> > > > > /* Check for stall activity */
> > > > > if (group->polling_total[t->state] == total[t->state])
> > > > > continue;
> > > > >
> > > > > /*
> > > > > - * Multiple triggers might be looking at the same state,
> > > > > - * remember to update group->polling_total[] once we've
> > > > > - * been through all of them. Also remember to extend the
> > > > > - * polling time if we see new stall activity.
> > > > > + * update the trigger if there is new stall which will be
> > > > > + * reset when run out of the window
> > > > > */
> > > > > - new_stall = true;
> > > > > + t->new_stall = true;
> > > > > +
> > > > > + memcpy(&group->polling_total[t->state], &total[t->state],
> > > > > + sizeof(group->polling_total[t->state]));
> > > > > + }
> > > > > +
> > > > > + list_for_each_entry(t, &group->triggers, node) {
> > > > > + u64 growth;
> > > > > +
> > > > > + /* check if new stall happened during this window*/
> > > > > + if (!t->new_stall)
> > > > > + continue;
> > > > >
> > > > > /* Calculate growth since last update */
> > > > > growth = window_update(&t->win, now, total[t->state]);
> > > > > @@ -552,10 +561,6 @@ static u64 update_triggers(struct psi_group *group, u64 now)
> > > > > t->last_event_time = now;
> > > > > }
> > > > >
> > > > > - if (new_stall)
> > > > > - memcpy(group->polling_total, total,
> > > > > - sizeof(group->polling_total));
> > > > > -
> > > > > return now + group->poll_min_period;
> > > > > }
> > > > >
> > > > > @@ -1152,6 +1157,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group,
> > > > > t->last_event_time = 0;
> > > > > init_waitqueue_head(&t->event_wait);
> > > > > kref_init(&t->refcount);
> > > > > + t->new_stall = false;
> > > > >
> > > > > mutex_lock(&group->trigger_lock);
> > > > >
> > > > > --
> > > > > 1.9.1
> > > > >
Powered by blists - more mailing lists