Messages in this thread | | | Date | Fri, 20 Nov 2020 23:17:24 +0100 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH 1/2] kthread: Move prio/affinite change into the newly created thread |
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On 2020-11-17 13:45:03 [+0100], Peter Zijlstra wrote: > On Tue, Nov 10, 2020 at 12:38:47PM +0100, Sebastian Andrzej Siewior wrote: > > With enabled threaded interrupts the nouveau driver reported the > > following: > > | Chain exists of: > > | &mm->mmap_lock#2 --> &device->mutex --> &cpuset_rwsem > > | > > | Possible unsafe locking scenario: > > | > > | CPU0 CPU1 > > | ---- ---- > > | lock(&cpuset_rwsem); > > | lock(&device->mutex); > > | lock(&cpuset_rwsem); > > | lock(&mm->mmap_lock#2); > > > > The device->mutex is nvkm_device::mutex. > > > > Unblocking the lockchain at `cpuset_rwsem' is probably the easiest thing > > to do. > > Move the priority reset to the start of the newly created thread. > > > > Fixes: 710da3c8ea7df ("sched/core: Prevent race condition between cpuset and __sched_setscheduler()") > > Reported-by: Mike Galbraith <efault@gmx.de> > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > > Link: https://lkml.kernel.org/r/a23a826af7c108ea5651e73b8fbae5e653f16e86.camel@gmx.de > > Moo... yes this is certainly the easiest solution, because nouveau is a > horrible rats nest. But when I spoke to Greg KH about this, he suggested > nouveau ought to be fixed. > > Ben, I got terminally lost when trying to untangle nouvea init, is there > any chance this can be fixed to not hold that nvkm_device::mutex thing > while doing request_irq() ?
Ben, did you had a chance to peek at this?
> > --- > > kernel/kthread.c | 16 ++++++++-------- > > 1 file changed, 8 insertions(+), 8 deletions(-) > > > > diff --git a/kernel/kthread.c b/kernel/kthread.c > > index 933a625621b8d..4a31127c6efbf 100644 > > --- a/kernel/kthread.c > > +++ b/kernel/kthread.c > > @@ -243,6 +243,7 @@ EXPORT_SYMBOL_GPL(kthread_parkme); > > > > static int kthread(void *_create) > > { > > + static const struct sched_param param = { .sched_priority = 0 }; > > /* Copy data: it's on kthread's stack */ > > struct kthread_create_info *create = _create; > > int (*threadfn)(void *data) = create->threadfn; > > @@ -273,6 +274,13 @@ static int kthread(void *_create) > > init_completion(&self->parked); > > current->vfork_done = &self->exited; > > > > + /* > > + * The new thread inherited kthreadd's priority and CPU mask. Reset > > + * back to default in case they have been changed. > > + */ > > + sched_setscheduler_nocheck(current, SCHED_NORMAL, ¶m); > > + set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_KTHREAD)); > > + > > /* OK, tell user we're spawned, wait for stop or wakeup */ > > __set_current_state(TASK_UNINTERRUPTIBLE); > > create->result = current; > > @@ -370,7 +378,6 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data), > > } > > task = create->result; > > if (!IS_ERR(task)) { > > - static const struct sched_param param = { .sched_priority = 0 }; > > char name[TASK_COMM_LEN]; > > > > /* > > @@ -379,13 +386,6 @@ struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data), > > */ > > vsnprintf(name, sizeof(name), namefmt, args); > > set_task_comm(task, name); > > - /* > > - * root may have changed our (kthreadd's) priority or CPU mask. > > - * The kernel thread should not inherit these properties. > > - */ > > - sched_setscheduler_nocheck(task, SCHED_NORMAL, ¶m); > > - set_cpus_allowed_ptr(task, > > - housekeeping_cpumask(HK_FLAG_KTHREAD)); > > } > > kfree(create); > > return task;
Sebastian
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