Re: [PATCH] driver core / ACPI: Avoid device removal locking problems

[Toshi Kani <toshi.kani@hp.com>]

On Wed, 2013-08-28 at 10:12 +0800, Gu Zheng wrote:
> On 08/28/2013 05:38 AM, Toshi Kani wrote:
 :
> >>
> >> What about changing device_hotplug_lock and acpi_scan_lock to rwsem? like the
> >> attached one(With a preliminary test, it also can make the splat go away).:)
> > 
> > I am curious how msleep(10) & restart_syscall() work in the change
> > below.  Doesn't the msleep() make s_active held longer time, which can
> > lead the thread holding device_hotplug_lock to wait it for deletion?
> 
> Yes, but it can avoid busy waiting. 

I know, but it's kinda unfortunate to sleep with s_active held in this
situation.  But I am fine with the 5ms Rafael used in this latest
patchset since this is a rare case anyway.

> > Also, does restart_syscall() release s_active and reopen this file
> > again?
> 
> Sure, it just set a TIF_SIGPENDING flag and return an -ERESTARTNOINTR error, s_active/file
> will be released/closed in the failed path. And when do_signal() catches the -ERESTARTNOINTR,
> it will change the regs to restart the syscall.

I see.  This is a clever functionality. 

Thanks,
-Toshi