[Intel-gfx] [PATCH] drm/i915: Convert WARNs during userptr revoke to SIGBUS

Tvrtko Ursulin tvrtko.ursulin at linux.intel.com
Fri Oct 9 02:03:14 PDT 2015

On 09/10/15 09:55, Daniel Vetter wrote:
> On Fri, Oct 09, 2015 at 09:40:53AM +0100, Chris Wilson wrote:
>> On Fri, Oct 09, 2015 at 09:48:01AM +0200, Daniel Vetter wrote:
>>> On Thu, Oct 08, 2015 at 10:45:47AM +0100, Tvrtko Ursulin wrote:
>>> The concern is that this isn't how SIG_SEGV works, it's a signal the
>>> thread who made the invalid access gets directly. You never get a SIG_SEGV
>>> for bad access someone else has made. So essentially it's new ABI.
>> SIGBUS. For which the answer is yes, you can and do get SIGBUS for
>> actions taken by other processes.
> Oh right I always forget that SIGBUS aliases with SIGIO. Anyway if
> userspace wants SIGIO we just need to provide it with a pollable fd and
> then it can use fcntl to make that happen. That's imo a much better api
> than unconditionally throwing around signals. Also we already have the
> reset stats ioctl to tell userspace that its gpu context is toats. If
> anyone wants that to be pollable (or even send SIGIO) I think we should
> extend that, with all the usual "needs userspace&igt" stuff on top.

I don't see that this notification can be optional. Process is confused 
about its memory map use so should die. :)

This is not a GPU error/hang - this is the process doing stupid things.

MMU notifiers do not support decision making otherwise we could say 
-ETXTBUSY or something on munmap, but we can't. Not even sure that it 
would help in all cases, would have to fail clone as well and who knows 



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