Am 19.02.2018 um 16:24 schrieb Daniel Vetter:
On Thu, Feb 15, 2018 at 03:19:42PM +0100, Christian König wrote:
amdgpu needs to verify if userspace sends us valid addresses and the simplest
way of doing this is to check if the buffer object is locked with the ticket
of the current submission.

Clean up the access to the ww_mutex internals by providing a function
for this and extend the check to the thread owning the underlying mutex.

Signed-off-by: Christian König <>
  drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c |  3 ++-
  include/linux/ww_mutex.h               | 17 +++++++++++++++++
  2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c 
index eaa3cb0c3ad1..4c04b560e358 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
@@ -1594,7 +1594,8 @@ int amdgpu_cs_find_mapping(struct amdgpu_cs_parser 
        *map = mapping;
/* Double check that the BO is reserved by this CS */
-       if (READ_ONCE((*bo)->tbo.resv->lock.ctx) != &parser->ticket)
+       if (!ww_mutex_is_owned_by(&(*bo)->tbo.resv->lock, current,
+                                 &parser->ticket))
                return -EINVAL;
if (!((*bo)->flags & AMDGPU_GEM_CREATE_VRAM_CONTIGUOUS)) {
diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index 39fda195bf78..dd580db289e8 100644
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -358,4 +358,21 @@ static inline bool ww_mutex_is_locked(struct ww_mutex 
        return mutex_is_locked(&lock->base);
+ * ww_mutex_is_owned_by - is the w/w mutex locked by this task in that context
+ * @lock: the mutex to be queried
+ * @task: the task structure to check
+ * @ctx: the w/w acquire context to test
+ *
+ * Returns true if the mutex is locked in the context by the given task, false
+ * otherwise.
+ */
+static inline bool ww_mutex_is_owned_by(struct ww_mutex *lock,
+                                       struct task_struct *task,
+                                       struct ww_acquire_ctx *ctx)
+       return likely(__mutex_owner(&lock->base) == task) &&
+               READ_ONCE(lock->ctx) == ctx;
Just comparing the context should be good enough. If you ever pass a
ww_acquire_ctx which does not belong to your own thread your seriously
wreaking things much worse already (and if we do catch that, should
probably lock the ctx to a given task when ww-mutex debugging is enabled).

That also simplifies the function signature.

Of course that means if you don't have a ctx, you can't test ownership of
a ww_mute, but I think that's not a really valid use-case.

Well exactly that is the use case in TTM, see patch #3 in this series.

In TTM the evicted BOs are trylocked and so we need a way of testing for ownership without a context.


  And not needed
for cmd submission, where you need the ctx anyway.

Besides this interface nit looks all good. With the task check&parameter

Reviewed-by: Daniel Vetter <>



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