| 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: <ZFPXSbjA7EQe4M1G@vingu-book>
Date: Thu, 4 May 2023 18:03:21 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Hao Jia <jiahao.os@...edance.com>
Cc: mingo@...hat.com, peterz@...radead.org, mingo@...nel.org,
juri.lelli@...hat.com, dietmar.eggemann@....com,
rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
bristot@...hat.com, vschneid@...hat.com,
mgorman@...hsingularity.net, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH 2/2] sched/core: Avoid double calling
update_rq_clock()
Le mardi 02 mai 2023 à 18:22:56 (+0800), Hao Jia a écrit :
>
>
> On 2023/4/21 Vincent Guittot wrote:
> > On Mon, 10 Apr 2023 at 10:12, Hao Jia <jiahao.os@...edance.com> wrote:
> > >
> > > There are some double rq clock update warnings are triggered.
> > > ------------[ cut here ]------------
> > > rq->clock_update_flags & RQCF_UPDATED
> > > WARNING: CPU: 17 PID: 138 at kernel/sched/core.c:741
> > > update_rq_clock+0xaf/0x180
> > > Call Trace:
> > > <TASK>
> > > __balance_push_cpu_stop+0x146/0x180
> > > ? migration_cpu_stop+0x2a0/0x2a0
> > > cpu_stopper_thread+0xa3/0x140
> > > smpboot_thread_fn+0x14f/0x210
> > > ? sort_range+0x20/0x20
> > > kthread+0xe6/0x110
> > > ? kthread_complete_and_exit+0x20/0x20
> > > ret_from_fork+0x1f/0x30
> > >
> > > ------------[ cut here ]------------
> > > rq->clock_update_flags & RQCF_UPDATED
> > > WARNING: CPU: 54 PID: 0 at kernel/sched/core.c:741
> > > update_rq_clock+0xaf/0x180
> > > Call Trace:
> > > <TASK>
> > > unthrottle_cfs_rq+0x4b/0x300
> > > __cfsb_csd_unthrottle+0xe0/0x100
> > > __flush_smp_call_function_queue+0xaf/0x1d0
> > > flush_smp_call_function_queue+0x49/0x90
> > > do_idle+0x17c/0x270
> > > cpu_startup_entry+0x19/0x20
> > > start_secondary+0xfa/0x120
> > > secondary_startup_64_no_verify+0xce/0xdb
> > >
> > > ------------[ cut here ]------------
> > > rq->clock_update_flags & RQCF_UPDATED
> > > WARNING: CPU: 0 PID: 3323 at kernel/sched/core.c:741
> > > update_rq_clock+0xaf/0x180
> > > Call Trace:
> > > <TASK>
> > > unthrottle_cfs_rq+0x4b/0x300
> > > rq_offline_fair+0x89/0x90
> > > set_rq_offline.part.118+0x28/0x60
> >
> > So this is generated by patch 1, isn't it ?
>
> Sorry for the late reply, I just got back from a long term.
>
> IIRC, this is not generated by patch1.
yeah, that's in the cfs loop
>
> In the unthrottle_offline_cfs_rqs() function, we traverse task_groups
> through list_for_each_entry_rcu, so unthrottle_cfs_rq() may be called
> multiple times, resulting in multiple updates to the rq clock.
>
> Thanks,
> Hao
> >
> > > rq_attach_root+0xc4/0xd0
> > > cpu_attach_domain+0x3dc/0x7f0
> > > partition_sched_domains_locked+0x2a5/0x3c0
> > > rebuild_sched_domains_locked+0x477/0x830
> > > rebuild_sched_domains+0x1b/0x30
> > > cpuset_hotplug_workfn+0x2ca/0xc90
> > > ? balance_push+0x56/0xf0
> > > ? _raw_spin_unlock+0x15/0x30
> > > ? finish_task_switch+0x98/0x2f0
> > > ? __switch_to+0x291/0x410
> > > ? __schedule+0x65e/0x1310
> > > process_one_work+0x1bc/0x3d0
> > > worker_thread+0x4c/0x380
> > > ? preempt_count_add+0x92/0xa0
> > > ? rescuer_thread+0x310/0x310
> > > kthread+0xe6/0x110
> > > ? kthread_complete_and_exit+0x20/0x20
> > > ret_from_fork+0x1f/0x30
> > >
> > > For the __balance_push_cpu_stop() case, we remove update_rq_clock() from
> > > the __migrate_task() function to avoid double updating the rq clock.
> > > And in order to avoid missing rq clock update, add update_rq_clock()
> > > call before migration_cpu_stop() calls __migrate_task().
Can we do the opposite ?
AFAICT, update_rq_clock() in __balance_push_cpu_stop() is only there for
__migrate_task(). I prefer to keep the update_rq_clock() as close as possible
to the user
> > >
> > > This also works for unthrottle_cfs_rq(), so we also removed
> > > update_rq_clock() from the unthrottle_cfs_rq() function to avoid
> > > warnings caused by calling it multiple times, such as
> > > __cfsb_csd_unthrottle() and unthrottle_offline_cfs_rqs(). and
This happens with the for loop added by
commit: 8ad075c2eb1f ("sched: Async unthrottling for cfs bandwidth")
> > > in order to avoid missing rq clock update, we correspondingly add
> > > update_rq_clock() calls before unthrottle_cfs_rq() runs.
These are special cases that happen because of the for_each.
As said above, I would prefer keeping update_rq_clock close the their user
could we use something similar to rq_clock_skip_update() for those list ?
Something like the below:
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 898fa3bc2765..7495b6fb229d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9386,8 +9386,6 @@ static int __balance_push_cpu_stop(void *arg)
raw_spin_lock_irq(&p->pi_lock);
rq_lock(rq, &rf);
- update_rq_clock(rq);
-
if (task_rq(p) == rq && task_on_rq_queued(p)) {
cpu = select_fallback_rq(rq->cpu, p);
rq = __migrate_task(rq, &rf, p, cpu);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 503b7617d7e1..a1d47d907360 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5518,6 +5518,12 @@ static void __cfsb_csd_unthrottle(void *arg)
struct rq_flags rf;
rq_lock(rq, &rf);
+ /*
+ * Iterating over the list can trigger several call to update_rq_clock.
+ * Do it once and skip the potential next ones.
+ */
+ update_rq_clock(rq);
+ rq_clock_loop_update(rq);
/*
* Since we hold rq lock we're safe from concurrent manipulation of
@@ -6058,6 +6064,13 @@ static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
lockdep_assert_rq_held(rq);
+ /*
+ * Iterating over the list can trigger several call to update_rq_clock.
+ * Do it once and skip the potential next ones.
+ */
+ update_rq_clock(rq);
+ rq_clock_loop_update(rq);
+
rcu_read_lock();
list_for_each_entry_rcu(tg, &task_groups, list) {
struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 66bacd50d381..681924367891 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1536,6 +1536,19 @@ static inline void rq_clock_skip_update(struct rq *rq)
rq->clock_update_flags |= RQCF_REQ_SKIP;
}
+/*
+ * During cpu offlining and rq wide unthrottling, we can trigger
+ * an update_rq_clock() for several cfs and rt runqueues (Typically
+ * when using list_for_each_entry_*)
+ * rq_clock_loop_update() can be called after updating the clock once
+ * and before iterating over the list to prevent multiple update.
+ */
+static inline void rq_clock_loop_update(struct rq *rq)
+{
+ lockdep_assert_rq_held(rq);
+ rq->clock_update_flags |= RQCF_ACT_SKIP;
+}
+
/*
* See rt task throttling, which is the only time a skip
* request is canceled.
> > >
> > > Note that the rq clock has been updated before the set_rq_offline()
> > > function runs, so we don't need to add update_rq_clock() call in
> > > unthrottle_offline_cfs_rqs().
> > >
>
>
>
Powered by blists - more mailing lists