On Tue 01 Sep 03:42 UTC 2020, Rob Clark wrote:

On Mon, Aug 31, 2020 at 7:35 PM Bjorn Andersson
[off-list ref] wrote:

quoted

On Fri 14 Aug 02:40 UTC 2020, Rob Clark wrote:

quoted

From: Rob Clark <redacted>

Currently it doesn't matter, since we free the ctx immediately.  But
when we start refcnt'ing the ctx, we don't want old dangling list
entries to hang around.

Signed-off-by: Rob Clark <redacted>
---
 drivers/gpu/drm/msm/msm_submitqueue.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/msm_submitqueue.c b/drivers/gpu/drm/msm/msm_submitqueue.c
index a1d94be7883a..90c9d84e6155 100644
--- a/drivers/gpu/drm/msm/msm_submitqueue.c
+++ b/drivers/gpu/drm/msm/msm_submitqueue.c

@@ -49,8 +49,10 @@ void msm_submitqueue_close(struct msm_file_private *ctx)
       * No lock needed in close and there won't
       * be any more user ioctls coming our way
       */
-     list_for_each_entry_safe(entry, tmp, &ctx->submitqueues, node)
+     list_for_each_entry_safe(entry, tmp, &ctx->submitqueues, node) {
+             list_del(&entry->node);

If you refcount ctx, what does that do for the entries in the submit
queue?

"entry" here is kref'ed, but you're popping it off the list regardless
of the put ends up freeing the object or not - which afaict would mean
leaking the object.

What ends up happening is the submit has reference to submit-queue,
which has reference to the ctx.. the submitqueue could be alive still
pending in-flight submits (in a later patch), but dead from the PoV of
userspace interface.

We aren't relying (or at least aren't in the end, and I *think* I
didn't miss anything in the middle) relying on ctx->submitqueues list
to clean anything up in the end, just track what is still a valid
submitqueue from userspace PoV

Looks reasonable, thanks for the explanation.

BR,
-R

quoted

On the other hand, with the current implementation an object with higher
refcount with adjacent objects of single refcount would end up with
dangling pointers after the put. So in itself this change seems like a
net gain, but I'm wondering about the plan described in the commit
message.

Regards,
Bjorn

quoted

              msm_submitqueue_put(entry);
+     }
 }

 int msm_submitqueue_create(struct drm_device *drm, struct msm_file_private *ctx,
--
2.26.2

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