Messages in this thread | | | Date | Tue, 17 Nov 2020 13:45:03 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/2] kthread: Move prio/affinite change into the newly created thread |
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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() ?
> --- > 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; > -- > 2.29.2 >
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