diff options
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/core.c | 4 | ||||
| -rw-r--r-- | kernel/sched/membarrier.c | 175 | ||||
| -rw-r--r-- | kernel/sched/sched.h | 34 |
3 files changed, 168 insertions, 45 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 84c71160beb1..2d9a3947bef4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3358,15 +3358,15 @@ context_switch(struct rq *rq, struct task_struct *prev, else prev->active_mm = NULL; } else { // to user + membarrier_switch_mm(rq, prev->active_mm, next->mm); /* * sys_membarrier() requires an smp_mb() between setting - * rq->curr and returning to userspace. + * rq->curr / membarrier_switch_mm() and returning to userspace. * * The below provides this either through switch_mm(), or in * case 'prev->active_mm == next->mm' through * finish_task_switch()'s mmdrop(). */ - switch_mm_irqs_off(prev->active_mm, next->mm, next); if (!prev->mm) { // from kernel diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index 7ccbd0e19626..070cf433bb9a 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -30,6 +30,39 @@ static void ipi_mb(void *info) smp_mb(); /* IPIs should be serializing but paranoid. */ } +static void ipi_sync_rq_state(void *info) +{ + struct mm_struct *mm = (struct mm_struct *) info; + + if (current->mm != mm) + return; + this_cpu_write(runqueues.membarrier_state, + atomic_read(&mm->membarrier_state)); + /* + * Issue a memory barrier after setting + * MEMBARRIER_STATE_GLOBAL_EXPEDITED in the current runqueue to + * guarantee that no memory access following registration is reordered + * before registration. + */ + smp_mb(); +} + +void membarrier_exec_mmap(struct mm_struct *mm) +{ + /* + * Issue a memory barrier before clearing membarrier_state to + * guarantee that no memory access prior to exec is reordered after + * clearing this state. + */ + smp_mb(); + atomic_set(&mm->membarrier_state, 0); + /* + * Keep the runqueue membarrier_state in sync with this mm + * membarrier_state. + */ + this_cpu_write(runqueues.membarrier_state, 0); +} + static int membarrier_global_expedited(void) { int cpu; @@ -56,6 +89,7 @@ static int membarrier_global_expedited(void) } cpus_read_lock(); + rcu_read_lock(); for_each_online_cpu(cpu) { struct task_struct *p; @@ -70,17 +104,25 @@ static int membarrier_global_expedited(void) if (cpu == raw_smp_processor_id()) continue; - rcu_read_lock(); + if (!(READ_ONCE(cpu_rq(cpu)->membarrier_state) & + MEMBARRIER_STATE_GLOBAL_EXPEDITED)) + continue; + + /* + * Skip the CPU if it runs a kernel thread. The scheduler + * leaves the prior task mm in place as an optimization when + * scheduling a kthread. + */ p = rcu_dereference(cpu_rq(cpu)->curr); - if (p && p->mm && (atomic_read(&p->mm->membarrier_state) & - MEMBARRIER_STATE_GLOBAL_EXPEDITED)) { - if (!fallback) - __cpumask_set_cpu(cpu, tmpmask); - else - smp_call_function_single(cpu, ipi_mb, NULL, 1); - } - rcu_read_unlock(); + if (p->flags & PF_KTHREAD) + continue; + + if (!fallback) + __cpumask_set_cpu(cpu, tmpmask); + else + smp_call_function_single(cpu, ipi_mb, NULL, 1); } + rcu_read_unlock(); if (!fallback) { preempt_disable(); smp_call_function_many(tmpmask, ipi_mb, NULL, 1); @@ -136,6 +178,7 @@ static int membarrier_private_expedited(int flags) } cpus_read_lock(); + rcu_read_lock(); for_each_online_cpu(cpu) { struct task_struct *p; @@ -157,8 +200,8 @@ static int membarrier_private_expedited(int flags) else smp_call_function_single(cpu, ipi_mb, NULL, 1); } - rcu_read_unlock(); } + rcu_read_unlock(); if (!fallback) { preempt_disable(); smp_call_function_many(tmpmask, ipi_mb, NULL, 1); @@ -177,32 +220,78 @@ static int membarrier_private_expedited(int flags) return 0; } +static int sync_runqueues_membarrier_state(struct mm_struct *mm) +{ + int membarrier_state = atomic_read(&mm->membarrier_state); + cpumask_var_t tmpmask; + int cpu; + + if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) { + this_cpu_write(runqueues.membarrier_state, membarrier_state); + + /* + * For single mm user, we can simply issue a memory barrier + * after setting MEMBARRIER_STATE_GLOBAL_EXPEDITED in the + * mm and in the current runqueue to guarantee that no memory + * access following registration is reordered before + * registration. + */ + smp_mb(); + return 0; + } + + if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL)) + return -ENOMEM; + + /* + * For mm with multiple users, we need to ensure all future + * scheduler executions will observe @mm's new membarrier + * state. + */ + synchronize_rcu(); + + /* + * For each cpu runqueue, if the task's mm match @mm, ensure that all + * @mm's membarrier state set bits are also set in in the runqueue's + * membarrier state. This ensures that a runqueue scheduling + * between threads which are users of @mm has its membarrier state + * updated. + */ + cpus_read_lock(); + rcu_read_lock(); + for_each_online_cpu(cpu) { + struct rq *rq = cpu_rq(cpu); + struct task_struct *p; + + p = rcu_dereference(&rq->curr); + if (p && p->mm == mm) + __cpumask_set_cpu(cpu, tmpmask); + } + rcu_read_unlock(); + + preempt_disable(); + smp_call_function_many(tmpmask, ipi_sync_rq_state, mm, 1); + preempt_enable(); + + free_cpumask_var(tmpmask); + cpus_read_unlock(); + + return 0; +} + static int membarrier_register_global_expedited(void) { struct task_struct *p = current; struct mm_struct *mm = p->mm; + int ret; if (atomic_read(&mm->membarrier_state) & MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY) return 0; atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state); - if (atomic_read(&mm->mm_users) == 1) { - /* - * For single mm user, single threaded process, we can - * simply issue a memory barrier after setting - * MEMBARRIER_STATE_GLOBAL_EXPEDITED to guarantee that - * no memory access following registration is reordered - * before registration. - */ - smp_mb(); - } else { - /* - * For multi-mm user threads, we need to ensure all - * future scheduler executions will observe the new - * thread flag state for this mm. - */ - synchronize_rcu(); - } + ret = sync_runqueues_membarrier_state(mm); + if (ret) + return ret; atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY, &mm->membarrier_state); @@ -213,12 +302,15 @@ static int membarrier_register_private_expedited(int flags) { struct task_struct *p = current; struct mm_struct *mm = p->mm; - int state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY; + int ready_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY, + set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED, + ret; if (flags & MEMBARRIER_FLAG_SYNC_CORE) { if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE)) return -EINVAL; - state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY; + ready_state = + MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY; } /* @@ -226,20 +318,15 @@ static int membarrier_register_private_expedited(int flags) * groups, which use the same mm. (CLONE_VM but not * CLONE_THREAD). */ - if ((atomic_read(&mm->membarrier_state) & state) == state) + if ((atomic_read(&mm->membarrier_state) & ready_state) == ready_state) return 0; - atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state); if (flags & MEMBARRIER_FLAG_SYNC_CORE) - atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE, - &mm->membarrier_state); - if (atomic_read(&mm->mm_users) != 1) { - /* - * Ensure all future scheduler executions will observe the - * new thread flag state for this process. - */ - synchronize_rcu(); - } - atomic_or(state, &mm->membarrier_state); + set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE; + atomic_or(set_state, &mm->membarrier_state); + ret = sync_runqueues_membarrier_state(mm); + if (ret) + return ret; + atomic_or(ready_state, &mm->membarrier_state); return 0; } @@ -253,8 +340,10 @@ static int membarrier_register_private_expedited(int flags) * command specified does not exist, not available on the running * kernel, or if the command argument is invalid, this system call * returns -EINVAL. For a given command, with flags argument set to 0, - * this system call is guaranteed to always return the same value until - * reboot. + * if this system call returns -ENOSYS or -EINVAL, it is guaranteed to + * always return the same value until reboot. In addition, it can return + * -ENOMEM if there is not enough memory available to perform the system + * call. * * All memory accesses performed in program order from each targeted thread * is guaranteed to be ordered with respect to sys_membarrier(). If we use diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index b3cb895d14a2..0db2c1b3361e 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -911,6 +911,10 @@ struct rq { atomic_t nr_iowait; +#ifdef CONFIG_MEMBARRIER + int membarrier_state; +#endif + #ifdef CONFIG_SMP struct root_domain *rd; struct sched_domain __rcu *sd; @@ -2438,3 +2442,33 @@ static inline bool sched_energy_enabled(void) static inline bool sched_energy_enabled(void) { return false; } #endif /* CONFIG_ENERGY_MODEL && CONFIG_CPU_FREQ_GOV_SCHEDUTIL */ + +#ifdef CONFIG_MEMBARRIER +/* + * The scheduler provides memory barriers required by membarrier between: + * - prior user-space memory accesses and store to rq->membarrier_state, + * - store to rq->membarrier_state and following user-space memory accesses. + * In the same way it provides those guarantees around store to rq->curr. + */ +static inline void membarrier_switch_mm(struct rq *rq, + struct mm_struct *prev_mm, + struct mm_struct *next_mm) +{ + int membarrier_state; + + if (prev_mm == next_mm) + return; + + membarrier_state = atomic_read(&next_mm->membarrier_state); + if (READ_ONCE(rq->membarrier_state) == membarrier_state) + return; + + WRITE_ONCE(rq->membarrier_state, membarrier_state); +} +#else +static inline void membarrier_switch_mm(struct rq *rq, + struct mm_struct *prev_mm, + struct mm_struct *next_mm) +{ +} +#endif |