Re: [Intel-gfx] [PATCH 04/11] drm/i915/perf: do not warn when OA buffer is already allocated

[Lionel Landwerlin]

On 26/03/18 13:00, Matthew Auld wrote:

On 26 March 2018 at 10:08, Lionel Landwerlin
 wrote:

If 2 processes race to open the perf stream, it's possible that one of them
will see that OA buffer has already been allocated, while a previous process
is still finishing to reprogram the hardware (on gen8+).

But we grab the perf.lock while opening the perf stream, and we only
allow one exclusive stream. Maybe I'm missing something?


Arg, you're right...
The locking situation is really not obvious in this file.
I think we can drop this patch.

Thanks!
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Re: [Intel-gfx] [PATCH 04/11] drm/i915/perf: do not warn when OA buffer is already allocated

[Matthew Auld]

On 26 March 2018 at 10:08, Lionel Landwerlin
 wrote:
> If 2 processes race to open the perf stream, it's possible that one of them
> will see that OA buffer has already been allocated, while a previous process
> is still finishing to reprogram the hardware (on gen8+).

But we grab the perf.lock while opening the perf stream, and we only
allow one exclusive stream. Maybe I'm missing something?
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[Intel-gfx] [PATCH 04/11] drm/i915/perf: do not warn when OA buffer is already allocated

[Lionel Landwerlin]

If 2 processes race to open the perf stream, it's possible that one of them
will see that OA buffer has already been allocated, while a previous process
is still finishing to reprogram the hardware (on gen8+).

The opening sequence has been reworked a few times and we probably lost
track of the order in which things are supposed to happen.

Signed-off-by: Lionel Landwerlin 
---
 drivers/gpu/drm/i915/i915_perf.c | 8 +---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index f15dda286cfe..86c18ba46816 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -1435,13 +1435,15 @@ static int alloc_oa_buffer(struct drm_i915_private 
*dev_priv)
struct i915_vma *vma;
int ret;
 
-   if (WARN_ON(dev_priv->perf.oa.oa_buffer.vma))
-   return -ENODEV;
-
ret = i915_mutex_lock_interruptible(_priv->drm);
if (ret)
return ret;
 
+   if (dev_priv->perf.oa.oa_buffer.vma) {
+   ret = -EBUSY;
+   goto unlock;
+   }
+
BUILD_BUG_ON_NOT_POWER_OF_2(OA_BUFFER_SIZE);
BUILD_BUG_ON(OA_BUFFER_SIZE < SZ_128K || OA_BUFFER_SIZE > SZ_16M);
 
-- 
2.16.3

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