This needs to explain in much more detail what is going on and why it is not a problem. E.g.: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.dong@xxxxxxxxx> Cc: John Harrison <John.C.Harrison@xxxxxxxxx> Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx> Cc: Daniel Vetter <daniel@xxxxxxxx> --- 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. + */
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)
