diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/rcu/tasks.h | 10 | ||||
| -rw-r--r-- | kernel/sched/core.c | 14 |
2 files changed, 17 insertions, 7 deletions
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 4dc56b6e27c0..ba3440a45b6d 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1747,6 +1747,16 @@ static void rcu_tasks_trace_pregp_step(struct list_head *hop) // allow safe access to the hop list. for_each_online_cpu(cpu) { rcu_read_lock(); + // Note that cpu_curr_snapshot() picks up the target + // CPU's current task while its runqueue is locked with + // an smp_mb__after_spinlock(). This ensures that either + // the grace-period kthread will see that task's read-side + // critical section or the task will see the updater's pre-GP + // accesses. The trailing smp_mb() in cpu_curr_snapshot() + // does not currently play a role other than simplify + // that function's ordering semantics. If these simplified + // ordering semantics continue to be redundant, that smp_mb() + // might be removed. t = cpu_curr_snapshot(cpu); if (rcu_tasks_trace_pertask_prep(t, true)) trc_add_holdout(t, hop); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index bcf2c4cc0522..05afa2932b5e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4467,12 +4467,7 @@ int task_call_func(struct task_struct *p, task_call_f func, void *arg) * @cpu: The CPU on which to snapshot the task. * * Returns the task_struct pointer of the task "currently" running on - * the specified CPU. If the same task is running on that CPU throughout, - * the return value will be a pointer to that task's task_struct structure. - * If the CPU did any context switches even vaguely concurrently with the - * execution of this function, the return value will be a pointer to the - * task_struct structure of a randomly chosen task that was running on - * that CPU somewhere around the time that this function was executing. + * the specified CPU. * * If the specified CPU was offline, the return value is whatever it * is, perhaps a pointer to the task_struct structure of that CPU's idle @@ -4486,11 +4481,16 @@ int task_call_func(struct task_struct *p, task_call_f func, void *arg) */ struct task_struct *cpu_curr_snapshot(int cpu) { + struct rq *rq = cpu_rq(cpu); struct task_struct *t; + struct rq_flags rf; - smp_mb(); /* Pairing determined by caller's synchronization design. */ + rq_lock_irqsave(rq, &rf); + smp_mb__after_spinlock(); /* Pairing determined by caller's synchronization design. */ t = rcu_dereference(cpu_curr(cpu)); + rq_unlock_irqrestore(rq, &rf); smp_mb(); /* Pairing determined by caller's synchronization design. */ + return t; } |