[PATCH 3.13 066/151] drm/i915: Do not dereference pointers from ring buffer in evict event

Kamal Mostafa kamal at canonical.com
Fri May 2 15:37:34 UTC 2014 -stable review patch.  If anyone has any objections, please let me know.


From: Steven Rostedt <rostedt at goodmis.org>

commit 9297ebf29ad9118edd6c0fedc84f03e35028827d upstream.

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 at gmail.com>
Fixes: bcccff847d1f "drm/i915: trace vm eviction instead of everything"
Signed-off-by: Steven Rostedt <rostedt at goodmis.org>
[danvet: Try to make it actually compile]
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 drivers/gpu/drm/i915/i915_trace.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
index 6e580c9..783ae08 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,
+			     __field(u32, dev)
 			     __field(struct i915_address_space *, vm)
+			   __entry->dev = vm->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)

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