On Wed, 13 May 2009, Jens Axboe wrote:
> On Tue, May 12 2009, Andrew Morton wrote:
> > On Thu, 07 May 2009 15:37:36 +0200 Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> >
> > > + for (i = 0; i < spd.nr_pages; i++) {
> > > + kunmap(pages[i]);
> >
> > It is deadlockable if any thread of control holds more than a single
> > kmap at a time.
> >
> > Because there are a finite number of kmaps available, and if one is
> > unavailable, kmap() waits for one to become free. If the number of
> > waiting threads equals the number of available slots, nobody makes any
> > progress.
Ouch.
>
> Good catch, that will not work reliably. I've applied the below.
Thanks.
The bigger problem is that the default_file_splice_write()
implementation in the other patch does the same (it calls
buf->ops->map() on all buffers).
Hmm. Simple solution would be to do a write() for each buffer. But
this only affects HIGHMEM kernels, so it's a bit pointless to do that
on all archs. Sigh...
Miklos
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