lkml.org 
[lkml]   [2012]   [Feb]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Bug in disk event polling
Hello, Alan.

On Sun, Feb 12, 2012 at 12:48:22PM -0500, Alan Stern wrote:
> > I think it would be better to use wq for most kthreads. A lot of them
> > aren't strictly correct in the way they deal with
> > kthread_should_stop() and freezing. kthread in general simply seems
> > way too difficult to use correctly.
>
> Maybe so, but getting rid of it at this point would be a big change.

Ooh, yeah, if we do it, it would be a gradual transition.

> Also, kthreads were originally considered more suitable for tasks that
> would need to run for a long time; is this no longer true?

wq no longer has problem w/ long running work items. The only
limiting parameter is max_active, which is primarily there to protect
against berserk cases.

> > > kthread_run() can be adjusted on a case-by-case basis, by inserting
> > > calls to set_freezable() and try_to_freeze() at the appropriate places.
> > > But what about async_schedule()?
> >
> > Given the stuff async is used for, maybe just make all async execution
> > freezable?
>
> That probably won't work. What if a driver relies on async thread
> execution to carry out its I/O?
>
> As another example, sd_probe() calls async_schedule(sd_probe_async,...)
> to handle the long-running parts of probing a SCSI disk. In turn,
> sd_remove() calls async_synchronize_full() to insure that probing is
> over before the device is unbound from sd.
>
> What happens if a hot-unpluggable disk drive is unplugged while the
> system is asleep? It's entirely possible that the bus subsystem's
> resume routine would see the device was gone and would try to
> unregister it. Then sd_remove would wait for the async thread
> to finish, which would never happen because the thread would be frozen
> and wouldn't be thawed until all the resume routines had finished.
>
> In this case, the proper solution is to have the SCSI prepare method
> call async_synchronize_full(). Other cases will require other
> solutions.

Hmmm.... I don't know then. :)

Thanks.

--
tejun


\
 
 \ /
  Last update: 2012-02-13 18:33    [W:0.069 / U:0.432 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site