The following commit has been merged into the sched/urgent branch of tip: Commit-ID: b1e8206582f9d680cff7d04828708c8b6ab32957 Gitweb: https://git.kernel.org/tip/b1e8206582f9d680cff7d04828708c8b6ab32957 Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> AuthorDate: Mon, 14 Feb 2022 10:16:57 +01:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Sat, 19 Feb 2022 11:11:05 +01:00 sched: Fix yet more sched_fork() races 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@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Tested-by: Tadeusz Struk <tadeusz.struk@xxxxxxxxxx> Tested-by: Zhang Qiao <zhangqiao22@xxxxxxxxxx> Tested-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx> Link: https://lkml.kernel.org/r/YgoeCbwj5mbCR0qA@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx --- include/linux/sched/task.h | 4 ++-- kernel/fork.c | 13 ++++++++++++- kernel/sched/core.c | 34 +++++++++++++++++++++------------- 3 files changed, 35 insertions(+), 16 deletions(-) diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h index b9198a1..e84e54d 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -54,8 +54,8 @@ extern asmlinkage void schedule_tail(struct task_struct *prev); 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); diff --git a/kernel/fork.c b/kernel/fork.c index d75a528..c607d23 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2267,6 +2267,17 @@ static __latent_entropy struct task_struct *copy_process( 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 @@ -2376,7 +2387,7 @@ static __latent_entropy struct task_struct *copy_process( 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); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index fcf0c18..9745613 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1214,9 +1214,8 @@ int tg_nop(struct task_group *tg, void *data) } #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; @@ -4407,7 +4406,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p) 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 @@ -4425,6 +4424,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p) init_entity_runnable_average(&p->se); + #ifdef CONFIG_SCHED_INFO if (likely(sched_info_on())) memset(&p->sched_info, 0, sizeof(p->sched_info)); @@ -4440,18 +4440,23 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p) 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); /* @@ -4462,7 +4467,10 @@ void sched_post_fork(struct task_struct *p, struct kernel_clone_args *kargs) 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); } @@ -6922,7 +6930,7 @@ void set_user_nice(struct task_struct *p, long nice) 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); @@ -7213,7 +7221,7 @@ static void __setscheduler_params(struct task_struct *p, */ p->rt_priority = attr->sched_priority; p->normal_prio = normal_prio(p); - set_load_weight(p); + set_load_weight(p, true); } /* @@ -9446,7 +9454,7 @@ 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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