On 8/11/2023 11:20, Zhanjun Dong wrote:
This attempts to avoid circular locking dependency between flush delayed
work and intel_gt_reset.
When intel_gt_reset was called, task will hold a lock.
To cacel delayed work here, the _sync version will also acquire a lock,
which might trigger the possible cirular locking dependency warning.
When intel_gt_reset called, reset_in_progress flag will be set, add code
to check the flag, call async verion if reset is in progress.
Signed-off-by: Zhanjun Dong<zhanjun.d...@intel.com>
Cc: John Harrison<john.c.harri...@intel.com>
Cc: Andi Shyti<andi.sh...@linux.intel.com>
Cc: Daniel Vetter<dan...@ffwll.ch>
---
drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index a0e3ef1c65d2..600388c849f7 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -1359,7 +1359,16 @@ static void guc_enable_busyness_worker(struct intel_guc
*guc)
static void guc_cancel_busyness_worker(struct intel_guc *guc)
{
- cancel_delayed_work_sync(&guc->timestamp.work);
+ /*
+ * When intel_gt_reset was called, task will hold a lock.
+ * To cacel delayed work here, the _sync version will also acquire a
lock, which might
+ * trigger the possible cirular locking dependency warning.
+ * Check the reset_in_progress flag, call async verion if reset is in
progress.
+ */
This needs to explain in much more detail what is going on and why it is
not a problem. E.g.:
The busyness worker needs to be cancelled. In general that means
using the synchronous cancel version to ensure that an in-progress
worker will not keep executing beyond whatever is happening that
needs the cancel. E.g. suspend, driver unload, etc. However, in the
case of a reset, the synchronous version is not required and can
trigger a false deadlock detection warning.
The business worker takes the reset mutex to protect against resets
interfering with it. However, it does a trylock and bails out if the
reset lock is already acquired. Thus there is no actual deadlock or
other concern with the worker running concurrently with a reset. So
an asynchronous cancel is safe in the case of a reset rather than a
driver unload or suspend type operation. On the other hand, if the
cancel_sync version is used when a reset is in progress then the
mutex deadlock detection sees the mutex being acquired through
multiple paths and complains.
So just don't bother. That keeps the detection code happy and is
safe because of the trylock code described above.
John.
+ if (guc_to_gt(guc)->uc.reset_in_progress)
+ cancel_delayed_work(&guc->timestamp.work);
+ else
+ cancel_delayed_work_sync(&guc->timestamp.work);
}
static void __reset_guc_busyness_stats(struct intel_guc *guc)
