Inside the general i915_oa_init_reg_state() we avoid using the
perf->mutex. However, we rely on perf->exclusive_stream being valid to
access at that point, and for that we have to control the race with
disabling perf. This relies on the disabling being a heavy barrier that
inspects all active contexts, after marking the perf->exclusive_stream
as not available. This should ensure that there are no more concurrent
accesses to the perf->exclusive_stream as we destroy it.
Mark up the races around the perf->exclusive_stream so that they stand
out much more. (And hopefully we will be running kcsan to start
validating that the only races we have are carefully controlled.)
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_perf.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index e34c79df6ebc..0838a12e2dc5 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -1405,8 +1405,10 @@ static void i915_oa_stream_destroy(struct i915_perf_stream *stream)
/*
* Unset exclusive_stream first, it will be checked while disabling
* the metric set on gen8+.
+ *
+ * See i915_oa_init_reg_state() and lrc_configure_all_contexts()
*/
- perf->exclusive_stream = NULL;
+ WRITE_ONCE(perf->exclusive_stream, NULL);
perf->ops.disable_metric_set(stream);
free_oa_buffer(stream);
@@ -2847,7 +2849,7 @@ static int i915_oa_stream_init(struct i915_perf_stream *stream,
goto err_oa_buf_alloc;
stream->ops = &i915_oa_stream_ops;
- perf->exclusive_stream = stream;
+ WRITE_ONCE(perf->exclusive_stream, stream);
ret = perf->ops.enable_metric_set(stream);
if (ret) {
@@ -2867,7 +2869,7 @@ static int i915_oa_stream_init(struct i915_perf_stream *stream,
return 0;
err_enable:
- perf->exclusive_stream = NULL;
+ WRITE_ONCE(perf->exclusive_stream, NULL);
perf->ops.disable_metric_set(stream);
free_oa_buffer(stream);
@@ -2893,12 +2895,11 @@ void i915_oa_init_reg_state(const struct intel_context *ce,
{
struct i915_perf_stream *stream;
- /* perf.exclusive_stream serialised by lrc_configure_all_contexts() */
-
if (engine->class != RENDER_CLASS)
return;
- stream = engine->i915->perf.exclusive_stream;
+ /* perf.exclusive_stream serialised by lrc_configure_all_contexts() */
+ stream = READ_ONCE(engine->i915->perf.exclusive_stream);
/*
* For gen12, only CTX_R_PWR_CLK_STATE needs update, but the caller
* is already doing that, so nothing to be done for gen12 here.
--
2.25.1
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