linux-kernel - Re: [PATCH] drm/i915: Do not dereference pointers from ring buffer in evict event

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Date:	Tue, 18 Mar 2014 11:31:36 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Ben Widawsky <ben@...dawsk.net>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Ramkumar Ramachandra <artagnon@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	stable <stable@...r.kernel.org>
Subject: Re: [PATCH] drm/i915: Do not dereference pointers from ring buffer
 in evict event

On Tue, 18 Mar 2014 11:27:37 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> The TP_printk() should never dereference any pointers, because the ring
> buffer can be read at some unknown time in the future. If a device no
> longer exists, it can cause a kernel oops. This also makes this
> event useless when saving the ring buffer in userspaces tools such as
> perf and trace-cmd.
> 
> The i915_gem_evict_vm dereferences the vm pointer which may also not
> exist when the ring buffer is read sometime in the future.
> 
> Link: http://lkml.kernel.org/r/1395095198-20034-3-git-send-email-artagnon@gmail.com
> Reported-by: Ramkumar Ramachandra <artagnon@...il.com> Cc:
> stable@...r.kernel.org # 3.13+

Bah, claw's mail is playing havoc with my line wraps. Please fix the
above when applying, or I can send anothe patch. Thanks :-)

I had to re-insert the patch due to it but didn't see the screw up with
the Cc of stable.

-- Steve

> Fixes: bcccff847d1f "drm/i915: trace vm eviction instead of everything"
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
> diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
> index 6e580c9..f3e8a90 100644
> --- a/drivers/gpu/drm/i915/i915_trace.h
> +++ b/drivers/gpu/drm/i915/i915_trace.h
> @@ -238,14 +238,16 @@ TRACE_EVENT(i915_gem_evict_vm,
>  	    TP_ARGS(vm),
>  
>  	    TP_STRUCT__entry(
> +			     __field(u32, dev)
>  			     __field(struct i915_address_space *, vm)
>  			    ),
>  
>  	    TP_fast_assign(
> +			   __entry->dev = dev->primary->index;
>  			   __entry->vm = vm;
>  			  ),
>  
> -	    TP_printk("dev=%d, vm=%p", __entry->vm->dev->primary->index, __entry->vm)
> +	    TP_printk("dev=%d, vm=%p", __entry->dev, __entry->vm)
>  );
>  
>  TRACE_EVENT(i915_gem_ring_sync_to,

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