Messages in this thread | | | Subject | Re: [patch 2/3] splice: implement default splice_read method | From | Miklos Szeredi <> | Date | Wed, 13 May 2009 11:01:43 +0200 |
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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@szeredi.hu> 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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