svn commit: r266775 - head/sys/x86/x86

Attilio Rao attilio at freebsd.org
Fri May 30 15:51:42 UTC 2014


On Fri, May 30, 2014 at 5:47 PM, John Baldwin <jhb at freebsd.org> wrote:
> On Friday, May 30, 2014 11:39:24 am Attilio Rao wrote:
>> On Fri, May 30, 2014 at 5:03 PM, John Baldwin <jhb at freebsd.org> wrote:
>> > On Friday, May 30, 2014 10:54:06 am Attilio Rao wrote:
>> >> On Tue, May 27, 2014 at 11:31 PM, Scott Long <scottl at freebsd.org> wrote:
>> >> > Author: scottl
>> >> > Date: Tue May 27 21:31:11 2014
>> >> > New Revision: 266775
>> >> > URL: http://svnweb.freebsd.org/changeset/base/266775
>> >> >
>> >> > Log:
>> >> >   Eliminate the fake contig_dmamap and replace it with a new flag,
>> >> >   BUS_DMA_KMEM_ALLOC.  They serve the same purpose, but using the flag
>> >> >   means that the map can be NULL again, which in turn enables significant
>> >> >   optimizations for the common case of no bouncing.
>> >>
>> >> While I think this is in general a good idea, unfortunately our
>> >> drivers do so many dumb things when freeing DMA allocated buffers that
>> >> having a NULL map is going to cause some "turbolence" and make such
>> >> bugs more visible.
>> >> An example is with ATA, where I think this fix is needed:
>> >> http://www.freebsd.org/~attilio/dmamem_free-ata.patch
>> >>
>> >> Otherwise, what can happen with bounce buffers, is that the allocated
>> >> memory via contig malloc was not going to be freed anytime.
>> >>
>> >> I tried to look around and I found questionable (read broken) code in
>> >> basically every driver which allocates DMA buffers, so I really don't
>> >> feel I want to fix the majority of our drivers. I just think such
>> >> paths are not excercised enough to be seen in practice often or the
>> >> bugs just get unnoticed.
>> >
>> > Eh, many maps for static allocations were already NULL and have been for a
>> > long time.  This is nothign new.  Plus, the diff you posted has a bug
>> > regardless of explicitly destroying a map created by bus_dmamem_alloc().
>>
>> Did you notice that I *removed* the destroy not *added*?
>
> Yes, my point was that that bug in the original code you are fixing was there
> regardless of Scott's change.

And when I did say something different?
I don't understand what's the point of your messages, besides showing
that you didn't read correctly my patch.

Attilio


-- 
Peace can only be achieved by understanding - A. Einstein


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