| 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: <CAEXW_YQNi42gahbSJ1skadh_8D+Ry6ZOmMqSU5BdidfCbmOtRg@mail.gmail.com>
Date: Thu, 31 Mar 2022 15:00:40 -0400
From: Joel Fernandes <joel@...lfernandes.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Guenter Roeck <groeck@...omium.org>
Subject: Re: [PATCH] sched/core: Fix forceidle balancing
Hi,
By the way, might be slightly related - we still see crashes with
pick_task_fair() in our kernel even with this change:
https://lkml.org/lkml/2020/11/17/2137
Is it possible that when doing pick_task_fair() especially on a remote
CPU, both the "cfs_rq->curr" and the rbtree's "left" be NULL with core
scheduling? In this case, se will be NULL and can cause crashes right?
I think the code assumes this can never happen.
+Guenter Roeck kindly debugged pick_task_fair() in a crash as
follows. Copying some details he mentioned in a bug report:
Assembler/source:
25: e8 4f 11 00 00 call 0x1179 ; se =
pick_next_entity(cfs_rq, curr);
2a:* 48 8b 98 60 01 00 00 mov 0x160(%rax),%rbx ; trapping
instruction [cfs_rq = group_cfs_rq(se);]
31: 48 85 db test %rbx,%rbx
34: 75 d1 jne 0x7
36: 48 89 c7 mov %rax,%rdi
At 2a: RAX = se == NULL after pick_next_entity(). Looking closely into
pick_next_entity(), it can indeed return NULL if curr is NULL and if
left in pick_next_entity() is NULL. Per line 7:, curr is in %r14 and
indeed 0.
Thoughts?
-Joel
On Wed, Mar 30, 2022 at 12:05 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
>
> Steve reported that ChromeOS encounters the forceidle balancer being
> ran from rt_mutex_setprio()'s balance_callback() invocation and
> explodes.
>
> Now, the forceidle balancer gets queued every time the idle task gets
> selected, set_next_task(), which is strictly too often.
> rt_mutex_setprio() also uses set_next_task() in the 'change' pattern:
>
> queued = task_on_rq_queued(p); /* p->on_rq == TASK_ON_RQ_QUEUED */
> running = task_current(rq, p); /* rq->curr == p */
>
> if (queued)
> dequeue_task(...);
> if (running)
> put_prev_task(...);
>
> /* change task properties */
>
> if (queued)
> enqueue_task(...);
> if (running)
> set_next_task(...);
>
> However, rt_mutex_setprio() will explicitly not run this pattern on
> the idle task (since priority boosting the idle task is quite insane).
> Most other 'change' pattern users are pidhash based and would also not
> apply to idle.
>
> Also, the change pattern doesn't contain a __balance_callback()
> invocation and hence we could have an out-of-band balance-callback,
> which *should* trigger the WARN in rq_pin_lock() (which guards against
> this exact anti-pattern).
>
> So while none of that explains how this happens, it does indicate that
> having it in set_next_task() might not be the most robust option.
>
> Instead, explicitly queue the forceidle balancer from pick_next_task()
> when it does indeed result in forceidle selection. Having it here,
> ensures it can only be triggered under the __schedule() rq->lock
> instance, and hence must be ran from that context.
>
> This also happens to clean up the code a little, so win-win.
>
> Fixes: d2dfa17bc7de ("sched: Trivial forced-newidle balancer")
> Reported-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> kernel/sched/core.c | 16 +++++++++++-----
> kernel/sched/idle.c | 1 -
> kernel/sched/sched.h | 6 ------
> 3 files changed, 11 insertions(+), 12 deletions(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5752,6 +5752,8 @@ static inline struct task_struct *pick_t
>
> extern void task_vruntime_update(struct rq *rq, struct task_struct *p, bool in_fi);
>
> +static void queue_core_balance(struct rq *rq);
> +
> static struct task_struct *
> pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> {
> @@ -5801,7 +5803,7 @@ pick_next_task(struct rq *rq, struct tas
> }
>
> rq->core_pick = NULL;
> - return next;
> + goto out;
> }
>
> put_prev_task_balance(rq, prev, rf);
> @@ -5851,7 +5853,7 @@ pick_next_task(struct rq *rq, struct tas
> */
> WARN_ON_ONCE(fi_before);
> task_vruntime_update(rq, next, false);
> - goto done;
> + goto out_set_next;
> }
> }
>
> @@ -5970,8 +5972,12 @@ pick_next_task(struct rq *rq, struct tas
> resched_curr(rq_i);
> }
>
> -done:
> +out_set_next:
> set_next_task(rq, next);
> +out:
> + if (rq->core->core_forceidle_count && next == rq->idle)
> + queue_core_balance(rq);
> +
> return next;
> }
>
> @@ -6066,7 +6072,7 @@ static void sched_core_balance(struct rq
>
> static DEFINE_PER_CPU(struct callback_head, core_balance_head);
>
> -void queue_core_balance(struct rq *rq)
> +static void queue_core_balance(struct rq *rq)
> {
> if (!sched_core_enabled(rq))
> return;
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -434,7 +434,6 @@ static void set_next_task_idle(struct rq
> {
> update_idle_core(rq);
> schedstat_inc(rq->sched_goidle);
> - queue_core_balance(rq);
> }
>
> #ifdef CONFIG_SMP
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1232,8 +1232,6 @@ static inline bool sched_group_cookie_ma
> return false;
> }
>
> -extern void queue_core_balance(struct rq *rq);
> -
> static inline bool sched_core_enqueued(struct task_struct *p)
> {
> return !RB_EMPTY_NODE(&p->core_node);
> @@ -1267,10 +1265,6 @@ static inline raw_spinlock_t *__rq_lockp
> return &rq->__lock;
> }
>
> -static inline void queue_core_balance(struct rq *rq)
> -{
> -}
> -
> static inline bool sched_cpu_cookie_match(struct rq *rq, struct task_struct *p)
> {
> return true;
Powered by blists - more mailing lists