| 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: <20221104022538.GK5600@paulmck-ThinkPad-P17-Gen-1>
Date: Thu, 3 Nov 2022 19:25:38 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Feng Tang <feng.tang@...el.com>
Cc: tglx@...utronix.de, linux-kernel@...r.kernel.org,
john.stultz@...aro.org, sboyd@...nel.org, corbet@....net,
Mark.Rutland@....com, maz@...nel.org, kernel-team@...a.com,
neeraju@...eaurora.org, ak@...ux.intel.com,
zhengjun.xing@...el.com, Waiman Long <longman@...hat.com>,
John Stultz <jstultz@...gle.com>
Subject: Re: [PATCH clocksource 2/2] clocksource: Exponential backoff for
load-induced bogus watchdog reads
On Fri, Nov 04, 2022 at 10:16:53AM +0800, Feng Tang wrote:
> On Wed, Nov 02, 2022 at 11:40:09AM -0700, Paul E. McKenney wrote:
> > The clocksource watchdog will reject measurements that are excessively
> > delayed, that is, by more than 1.5 seconds beyond the intended 0.5-second
> > watchdog interval. On an extremely busy system, this can result in a
> > console message being printed every two seconds. This is excessively
> > noisy for a non-error condition.
> >
> > Therefore, apply exponential backoff to these messages. This exponential
> > backoff is capped at 1024 times the watchdog interval, which comes to
> > not quite one message per ten minutes.
> >
> > Please note that the bogus watchdog reads that occur when the watchdog
> > interval is less than 0.125 seconds are still printed unconditionally
> > because these likely correspond to a serious error condition in the
> > timer code or hardware.
>
> I saw there is ongoing discussion about some wording, overall it
> looks good to me, thanks!
>
> Reviewed-by: Feng Tang <feng.tang@...el.com>
Thank you! I will apply both of your Reviewed-by tags on the next rebase,
by which time hopefully Waiman and I come to agreement on wording. ;-)
Thanx, Paul
> > [ paulmck: Apply Feng Tang feedback. ]
> >
> > Reported-by: Waiman Long <longman@...hat.com>
> > Reported-by: Feng Tang <feng.tang@...el.com>
> > Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> > Cc: John Stultz <jstultz@...gle.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Stephen Boyd <sboyd@...nel.org>
> > Cc: Feng Tang <feng.tang@...el.com>
> > Cc: Waiman Long <longman@...hat.com>
> > ---
> > include/linux/clocksource.h | 4 ++++
> > kernel/time/clocksource.c | 31 +++++++++++++++++++++++++------
> > 2 files changed, 29 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
> > index 1d42d4b173271..daac05aedf56a 100644
> > --- a/include/linux/clocksource.h
> > +++ b/include/linux/clocksource.h
> > @@ -125,6 +125,10 @@ struct clocksource {
> > struct list_head wd_list;
> > u64 cs_last;
> > u64 wd_last;
> > + u64 wd_last_bogus;
> > + int wd_bogus_shift;
> > + unsigned long wd_bogus_count;
> > + unsigned long wd_bogus_count_last;
> > #endif
> > struct module *owner;
> > };
> > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> > index 3f5317faf891f..de8047b6720f5 100644
> > --- a/kernel/time/clocksource.c
> > +++ b/kernel/time/clocksource.c
> > @@ -442,14 +442,33 @@ static void clocksource_watchdog(struct timer_list *unused)
> >
> > /* Check for bogus measurements. */
> > wdi = jiffies_to_nsecs(WATCHDOG_INTERVAL);
> > - if (wd_nsec < (wdi >> 2)) {
> > - /* This usually indicates broken timer code or hardware. */
> > - pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced only %lld ns during %d-jiffy time interval, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL);
> > + if (wd_nsec > (wdi << 2) || cs_nsec > (wdi << 2)) {
> > + bool needwarn = false;
> > + u64 wd_lb;
> > +
> > + cs->wd_bogus_count++;
> > + if (!cs->wd_bogus_shift) {
> > + needwarn = true;
> > + } else {
> > + delta = clocksource_delta(wdnow, cs->wd_last_bogus, watchdog->mask);
> > + wd_lb = clocksource_cyc2ns(delta, watchdog->mult, watchdog->shift);
> > + if ((1 << cs->wd_bogus_shift) * wdi <= wd_lb)
> > + needwarn = true;
> > + }
> > + if (needwarn) {
> > + /* This can happen on busy systems, which can delay the watchdog. */
> > + pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced an excessive %lld ns during %d-jiffy time interval (%lu additional), probable CPU overutilization, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL, cs->wd_bogus_count - cs->wd_bogus_count_last);
> > + cs->wd_last_bogus = wdnow;
> > + if (cs->wd_bogus_shift < 10)
> > + cs->wd_bogus_shift++;
> > + cs->wd_bogus_count_last = cs->wd_bogus_count;
> > + }
> > continue;
> > }
> > - if (wd_nsec > (wdi << 2)) {
> > - /* This can happen on busy systems, which can delay the watchdog. */
> > - pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced an excessive %lld ns during %d-jiffy time interval, probable CPU overutilization, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL);
> > + /* Check too-short measurements second to handle wrap. */
> > + if (wd_nsec < (wdi >> 2) || cs_nsec < (wdi >> 2)) {
> > + /* This usually indicates broken timer code or hardware. */
> > + pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced only %lld ns during %d-jiffy time interval, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL);
> > continue;
> > }
> >
> > --
> > 2.31.1.189.g2e36527f23
> >
Powered by blists - more mailing lists