On 7/26/24 11:56 PM, Frederic Weisbecker wrote: > Make sure the kthread is sleeping in the schedule_preempt_disabled() > call before calling its handler when kthread_bind[_mask]() is called > on it. This provides a sanity check verifying that the task is not > randomly blocked later at some point within its function handler, in > which case it could be just concurrently awaken, leaving the call to > do_set_cpus_allowed() without any effect until the next voluntary sleep. > > Rely on the wake-up ordering to ensure that the newly introduced "started" > field returns the expected value: > > TASK A TASK B > ------ ------ > READ kthread->started > wake_up_process(B) > rq_lock() > ... > rq_unlock() // RELEASE > schedule() > rq_lock() // ACQUIRE > // schedule task B > rq_unlock() > WRITE kthread->started > > Similarly, writing kthread->started before subsequent voluntary sleeps > will be visible after calling wait_task_inactive() in > __kthread_bind_mask(), reporting potential misuse of the API. > > Upcoming patches will make further use of this facility. > > Signed-off-by: Frederic Weisbecker <[email protected]>
Acked-by: Vlastimil Babka <[email protected]> > --- > kernel/kthread.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/kthread.c b/kernel/kthread.c > index f7be976ff88a..ecb719f54f7a 100644 > --- a/kernel/kthread.c > +++ b/kernel/kthread.c > @@ -53,6 +53,7 @@ struct kthread_create_info > struct kthread { > unsigned long flags; > unsigned int cpu; > + int started; > int result; > int (*threadfn)(void *); > void *data; > @@ -382,6 +383,8 @@ static int kthread(void *_create) > schedule_preempt_disabled(); > preempt_enable(); > > + self->started = 1; > + > ret = -EINTR; > if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) { > cgroup_kthread_ready(); > @@ -540,7 +543,9 @@ static void __kthread_bind(struct task_struct *p, > unsigned int cpu, unsigned int > > void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask) > { > + struct kthread *kthread = to_kthread(p); > __kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE); > + WARN_ON_ONCE(kthread->started); > } > > /** > @@ -554,7 +559,9 @@ void kthread_bind_mask(struct task_struct *p, const > struct cpumask *mask) > */ > void kthread_bind(struct task_struct *p, unsigned int cpu) > { > + struct kthread *kthread = to_kthread(p); > __kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE); > + WARN_ON_ONCE(kthread->started); > } > EXPORT_SYMBOL(kthread_bind); >
