[PATCH v2] drm/i915: Do not dereference pointers from ring buffer in evict event

From: Steven Rostedt
Date: Tue Mar 18 2014 - 21:26:21 EST

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@xxxxxxxxx
Reported-by: Ramkumar Ramachandra <artagnon@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 3.13+
Fixes: bcccff847d1f "drm/i915: trace vm eviction instead of everything"
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
v2 - fixed build bug. This time tested on a box with an i915.

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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