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Date: Fri, 18 Feb 2022 14:18:42 +0800
From: Zhang Qiao <zhangqiao22@...wei.com>
To: Peter Zijlstra <peterz@...radead.org>,
Linus Torvalds <torvalds@...ux-foundation.org>
CC: Borislav Petkov <bp@...e.de>,
Tadeusz Struk <tadeusz.struk@...aro.org>,
x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
<tj@...nel.org>, <dietmar.eggemann@....com>
Subject: Re: [PATCH] sched: Fix yet more sched_fork() races
在 2022/2/17 16:51, Peter Zijlstra 写道:
> On Mon, Feb 14, 2022 at 10:16:57AM +0100, Peter Zijlstra wrote:
>> Zhang, Tadeusz, TJ, how does this look?
>
> *sigh* I was hoping for some Tested-by, since I've no idea how to
> operate this cgroup stuff properly.
tested this patch successfully.
Tested-by: Zhang Qiao <zhangqiao22@...wei.com>
>
> Anyway, full patch below. I'll go stick it in sched/urgent.
>
> ---
> Subject: sched: Fix yet more sched_fork() races
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Mon, 14 Feb 2022 10:16:57 +0100
>
> Where commit 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an
> invalid sched_task_group") fixed a fork race vs cgroup, it opened up a
> race vs syscalls by not placing the task on the runqueue before it
> gets exposed through the pidhash.
>
> Commit 13765de8148f ("sched/fair: Fix fault in reweight_entity") is
> trying to fix a single instance of this, instead fix the whole class
> of issues, effectively reverting this commit.
>
> Fixes: 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid sched_task_group")
> Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> include/linux/sched/task.h | 4 ++--
> kernel/fork.c | 13 ++++++++++++-
> kernel/sched/core.c | 34 +++++++++++++++++++++-------------
> 3 files changed, 35 insertions(+), 16 deletions(-)
>
> --- a/include/linux/sched/task.h
> +++ b/include/linux/sched/task.h
> @@ -54,8 +54,8 @@ extern asmlinkage void schedule_tail(str
> extern void init_idle(struct task_struct *idle, int cpu);
>
> extern int sched_fork(unsigned long clone_flags, struct task_struct *p);
> -extern void sched_post_fork(struct task_struct *p,
> - struct kernel_clone_args *kargs);
> +extern void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs);
> +extern void sched_post_fork(struct task_struct *p);
> extern void sched_dead(struct task_struct *p);
>
> void __noreturn do_task_dead(void);
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -2266,6 +2266,17 @@ static __latent_entropy struct task_stru
> goto bad_fork_put_pidfd;
>
> /*
> + * Now that the cgroups are pinned, re-clone the parent cgroup and put
> + * the new task on the correct runqueue. All this *before* the task
> + * becomes visible.
> + *
> + * This isn't part of ->can_fork() because while the re-cloning is
> + * cgroup specific, it unconditionally needs to place the task on a
> + * runqueue.
> + */
> + sched_cgroup_fork(p, args);
> +
> + /*
> * From this point on we must avoid any synchronous user-space
> * communication until we take the tasklist-lock. In particular, we do
> * not want user-space to be able to predict the process start-time by
> @@ -2375,7 +2386,7 @@ static __latent_entropy struct task_stru
> write_unlock_irq(&tasklist_lock);
>
> proc_fork_connector(p);
> - sched_post_fork(p, args);
> + sched_post_fork(p);
> cgroup_post_fork(p, args);
> perf_event_fork(p);
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1215,9 +1215,8 @@ int tg_nop(struct task_group *tg, void *
> }
> #endif
>
> -static void set_load_weight(struct task_struct *p)
> +static void set_load_weight(struct task_struct *p, bool update_load)
> {
> - bool update_load = !(READ_ONCE(p->__state) & TASK_NEW);
> int prio = p->static_prio - MAX_RT_PRIO;
> struct load_weight *load = &p->se.load;
>
> @@ -4408,7 +4407,7 @@ int sched_fork(unsigned long clone_flags
> p->static_prio = NICE_TO_PRIO(0);
>
> p->prio = p->normal_prio = p->static_prio;
> - set_load_weight(p);
> + set_load_weight(p, false);
>
> /*
> * We don't need the reset flag anymore after the fork. It has
> @@ -4426,6 +4425,7 @@ int sched_fork(unsigned long clone_flags
>
> init_entity_runnable_average(&p->se);
>
> +
> #ifdef CONFIG_SCHED_INFO
> if (likely(sched_info_on()))
> memset(&p->sched_info, 0, sizeof(p->sched_info));
> @@ -4441,18 +4441,23 @@ int sched_fork(unsigned long clone_flags
> return 0;
> }
>
> -void sched_post_fork(struct task_struct *p, struct kernel_clone_args *kargs)
> +void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs)
> {
> unsigned long flags;
> -#ifdef CONFIG_CGROUP_SCHED
> - struct task_group *tg;
> -#endif
>
> + /*
> + * Because we're not yet on the pid-hash, p->pi_lock isn't strictly
> + * required yet, but lockdep gets upset if rules are violated.
> + */
> raw_spin_lock_irqsave(&p->pi_lock, flags);
> #ifdef CONFIG_CGROUP_SCHED
> - tg = container_of(kargs->cset->subsys[cpu_cgrp_id],
> - struct task_group, css);
> - p->sched_task_group = autogroup_task_group(p, tg);
> + if (1) {
> + struct task_group *tg;
> + tg = container_of(kargs->cset->subsys[cpu_cgrp_id],
> + struct task_group, css);
> + tg = autogroup_task_group(p, tg);
> + p->sched_task_group = tg;
> + }
> #endif
> rseq_migrate(p);
> /*
> @@ -4463,7 +4468,10 @@ void sched_post_fork(struct task_struct
> if (p->sched_class->task_fork)
> p->sched_class->task_fork(p);
> raw_spin_unlock_irqrestore(&p->pi_lock, flags);
> +}
>
> +void sched_post_fork(struct task_struct *p)
> +{
> uclamp_post_fork(p);
> }
>
> @@ -6923,7 +6931,7 @@ void set_user_nice(struct task_struct *p
> put_prev_task(rq, p);
>
> p->static_prio = NICE_TO_PRIO(nice);
> - set_load_weight(p);
> + set_load_weight(p, true);
> old_prio = p->prio;
> p->prio = effective_prio(p);
>
> @@ -7214,7 +7222,7 @@ static void __setscheduler_params(struct
> */
> p->rt_priority = attr->sched_priority;
> p->normal_prio = normal_prio(p);
> - set_load_weight(p);
> + set_load_weight(p, true);
> }
>
> /*
> @@ -9447,7 +9455,7 @@ void __init sched_init(void)
> #endif
> }
>
> - set_load_weight(&init_task);
> + set_load_weight(&init_task, false);
>
> /*
> * The boot idle thread does lazy MMU switching as well:
>
> .
>
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