linux-kernel - Re: [Intel-gfx] [PATCH v2 5/5] tools/testing/scatterlist: Test new __sg_alloc_table_from

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Date:   Wed, 06 Sep 2017 13:39:32 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        "Tvrtko Ursulin" <tursulin@...ulin.net>,
        Intel-gfx@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [Intel-gfx] [PATCH v2 5/5] tools/testing/scatterlist: Test new
 __sg_alloc_table_from_pages

Quoting Tvrtko Ursulin (2017-09-06 13:10:57)
> 
> On 06/09/2017 11:48, Chris Wilson wrote:
> > All ascending. Interesting challenge for 3,2,1,0; it can be coalesced,
> > we just don't. I wonder if we are missing some like that. But for the
> 
> Hm, how do you think descending pages could be coalesced? By 
> re-arranging the pages? But that would break everything, do I don't get it.

Wishful thinking; I wasn't considering the order inside the object, just
their physical addresses.
> 
> > moment, 0, 2, 1, would be a good addition to the above set.
> > 
> > Is there any value in checking overflows in this interface?
> 
> Overflows as in size > num_pages * PAGE_SIZE as passed in to 
> __sg_alloc_table_from_pages ? It is not checked in the implementation at 
> the moment and it looks it is harmless.

Just thinking aloud if there was a way to get a mult/add overflow. That
we do page size coalescing, the only avenue is from a buggy max_seg.

Going back to the makefile, perhaps add the magic for ubsan as well?
-fsanitize=address -fsanitize=undefined
-Chris