| Message ID | 20240726215701.19459-12-frederic@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | None | expand |
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 <frederic@kernel.org> Acked-by: Vlastimil Babka <vbabka@suse.cz> > --- > 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); >
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);
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 <frederic@kernel.org> --- kernel/kthread.c | 7 +++++++ 1 file changed, 7 insertions(+)