Re: [PATCH 2/3] s390/vfio-ap: introduce two new r/w locks to replace wait_queue_head_t

Jason Gunthorpe
2021-06-11T17:41:54Z

On Fri, Jun 11, 2021 at 07:11:50PM +0200, David Hildenbrand wrote:

> > Also, not convinced down_write_trylock() is appropriate from a sysfs
> > callback, it should block and wait, surely? Otherwise userspace gets
> > random racy failures depending on what the kernel is doing??
>
> It might we worth exploring lock_device_hotplug_sysfs() which does a
>
> "return restart_syscall()" with some delay.

The ideal design from a sysfs should be a single
down_write_killable().

restart_syscall will just create a weird spinlock that is hopefully
unlikely to spin :\

Jason