On 01/03/2016 10:02, Joonas Lahtinen wrote:
The locking here is just the driver mutex lock. Whereas the test will only go bang if in atomic context (spinlock, IRQ, etc.). So it should be safe. If it isn't then the driver is already broken because the whole point of _wait_request() is that it will sleep! Although one could argue it is already broken because it quite likes sleeping with the mutex lock held.On to, 2016-02-18 at 14:27 +0000, John.C.Harrison@xxxxxxxxx wrote:From: John Harrison <John.C.Harrison@xxxxxxxxx> The scheduler can cause batch buffers, and hence requests, to be submitted to the ring out of order and asynchronously to their submission to the driver. Thus at the point of waiting for the completion of a given request, it is not even guaranteed that the request has actually been sent to the hardware yet. Even it is has been sent, it is possible that it could be pre-empted and thus 'unsent'. This means that it is necessary to be able to submit requests to the hardware during the wait call itself. Unfortunately, while some callers of __wait_request() release the mutex lock first, others do not (and apparently can not). Hence there is the ability to deadlock as the wait stalls for submission but the asynchronous submission is stalled for the mutex lock. This change hooks the scheduler in to the __wait_request() code to ensure correct behaviour. That is, flush the target batch buffer through to the hardware and do not deadlock waiting for something that cannot currently be submitted. Instead, the wait call must return EAGAIN at least as far back as necessary to release the mutex lock and allow the scheduler's asynchronous processing to get in and handle the pre-emption operation and eventually (re-)submit the work. v3: Removed the explicit scheduler flush from i915_wait_request(). This is no longer necessary and was causing unintended changes to the scheduler priority level which broke a validation team test. v4: Corrected the format of some comments to keep the style checker happy. v5: Added function description. [Joonas Lahtinen] For: VIZ-1587 Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> --- drivers/gpu/drm/i915/i915_drv.h | 3 ++- drivers/gpu/drm/i915/i915_gem.c | 37 ++++++++++++++++++++++++++------- drivers/gpu/drm/i915/i915_scheduler.c | 31 +++++++++++++++++++++++++++ drivers/gpu/drm/i915/i915_scheduler.h | 2 ++ drivers/gpu/drm/i915/intel_display.c | 5 +++-- drivers/gpu/drm/i915/intel_ringbuffer.c | 2 +- 6 files changed, 69 insertions(+), 11 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index 4d544f1..5eeeced 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -3071,7 +3071,8 @@ int __i915_wait_request(struct drm_i915_gem_request *req, unsigned reset_counter, bool interruptible, s64 *timeout, - struct intel_rps_client *rps); + struct intel_rps_client *rps, + bool is_locked);Multiple bool parameters are better converted to int flags, it makes the callsite code more readable if you have enum I915_WAIT_REQ_* flags.int __must_check i915_wait_request(struct drm_i915_gem_request *req); int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf); int __must_check diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 2dd9b55..17b44b3 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -1258,7 +1258,8 @@ int __i915_wait_request(struct drm_i915_gem_request *req, unsigned reset_counter, bool interruptible, s64 *timeout, - struct intel_rps_client *rps) + struct intel_rps_client *rps, + bool is_locked) { struct intel_engine_cs *ring = i915_gem_request_get_ring(req); struct drm_device *dev = ring->dev; @@ -1268,8 +1269,10 @@ int __i915_wait_request(struct drm_i915_gem_request *req, DEFINE_WAIT(wait); unsigned long timeout_expire; s64 before = 0; /* Only to silence a compiler warning. */ - int ret; + int ret = 0; + bool busy;Strange whitespace.+ might_sleep();This will splat if is_locked is true? So maybe it should be protected by if (!is_locked)?
I don't see what you mean. You can't take away all the timeout/sleeping related stuff, that is the whole point of the function! Everything that is inside the loop needs to be inside the loop. It is a hideously complicated wait function but as far as I can tell, it needs to be such. I recall at some point someone did a refactor to move the contents of the loop into a separate function but that doesn't seem to have made it upstream. Or maybe it did and it has since been reverted?WARN(!intel_irqs_enabled(dev_priv), "IRQs disabled");if (i915_gem_request_completed(req))@@ -1324,6 +1327,26 @@ int __i915_wait_request(struct drm_i915_gem_request *req, break; }+ if (is_locked) {+ /* + * If this request is being processed by the scheduler + * then it is unsafe to sleep with the mutex lock held + * as the scheduler may require the lock in order to + * progress the request. + */This is becoming a monstrous function, I think it could be split down to two functions, __i915_wait_request and __i915_wait_request_locked/nonblocking, because if you take all the timeout/sleeping related stuff away, not much is left.
The scheduler addition is now much simpler due to the re-implementing of the _is_tracked() function - see comments below.
It might have changed. The sleep might have been aborted due to something that means the scheduler is now busy and sleeping with the mutex lock held will cause a deadlock.+ if (i915_scheduler_is_request_tracked(req, NULL, &busy)) { + if (busy) { + ret = -EAGAIN; + break; + } + }If this is kept in single function, would not it be enough to execute this before the loop?
Yeah, the original need has actually changed somewhat since this was written. There is no longer any code which requires all three items together. So I've split it into two simpler functions which are more appropriate to their use cases.+ + /* + * If the request is not tracked by the scheduler + * then the regular test can be done. + */ + } + if (i915_gem_request_completed(req)) { ret = 0; break; @@ -1542,7 +1565,7 @@ i915_wait_request(struct drm_i915_gem_request *req)ret = __i915_wait_request(req,atomic_read(&dev_priv->gpu_error.reset_counter), - interruptible, NULL, NULL); + interruptible, NULL, NULL, true); if (ret) return ret;@@ -1655,7 +1678,7 @@ i915_gem_object_wait_rendering__nonblocking(struct drm_i915_gem_object *obj,mutex_unlock(&dev->struct_mutex); for (i = 0; ret == 0 && i < n; i++) ret = __i915_wait_request(requests[i], reset_counter, true, - NULL, rps); + NULL, rps, false); mutex_lock(&dev->struct_mutex);for (i = 0; i < n; i++) {@@ -3511,7 +3534,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file) if (ret == 0) ret = __i915_wait_request(req[i], reset_counter, true, args->timeout_ns > 0 ? &args->timeout_ns : NULL, - to_rps_client(file)); + to_rps_client(file), false); i915_gem_request_unreference(req[i]); } return ret; @@ -3544,7 +3567,7 @@ __i915_gem_object_sync(struct drm_i915_gem_object *obj, atomic_read(&i915->gpu_error.reset_counter), i915->mm.interruptible, NULL, - &i915->rps.semaphores); + &i915->rps.semaphores, true); if (ret) return ret;@@ -4523,7 +4546,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)if (target == NULL) return 0;- ret = __i915_wait_request(target, reset_counter, true, NULL, NULL);+ ret = __i915_wait_request(target, reset_counter, true, NULL, NULL, false); if (ret == 0) queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work, 0);diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.cindex 60a59d3..edab63d 100644 --- a/drivers/gpu/drm/i915/i915_scheduler.c +++ b/drivers/gpu/drm/i915/i915_scheduler.c @@ -918,6 +918,37 @@ void i915_scheduler_work_handler(struct work_struct *work) }/**+ * i915_scheduler_is_request_tracked - return info to say what the scheduler's + * connection to this request is (if any). + * @req: request to be queried + * @compeleted: if non-null, set to completion status + * @busy: if non-null set to busy status + * + * Looks up the given request in the scheduler's internal queue and reports + * on whether the request has completed or is still pending. + * Returns true if the request was found or false if it was not. + */ +bool i915_scheduler_is_request_tracked(struct drm_i915_gem_request *req, + bool *completed, bool *busy) +{ + struct drm_i915_private *dev_priv = req->ring->dev->dev_private; + struct i915_scheduler *scheduler = dev_priv->scheduler; + + if (!scheduler) + return false; + + if (req->scheduler_qe == NULL) + return false; +These better be their own functions, making the code more readable. _is_request_completed() _is_request_busy()
+ if (completed) + *completed = I915_SQS_IS_COMPLETE(req->scheduler_qe); + if (busy) + *busy = I915_SQS_IS_QUEUED(req->scheduler_qe); + + return true; +} + +/** * i915_scheduler_closefile - notify the scheduler that a DRM file handle * has been closed. * @dev: DRM device diff --git a/drivers/gpu/drm/i915/i915_scheduler.h b/drivers/gpu/drm/i915/i915_scheduler.h index 180d75f..a88adce 100644 --- a/drivers/gpu/drm/i915/i915_scheduler.h +++ b/drivers/gpu/drm/i915/i915_scheduler.h @@ -94,5 +94,7 @@ int i915_scheduler_queue_execbuffer(struct i915_scheduler_queue_entry *qe); bool i915_scheduler_notify_request(struct drm_i915_gem_request *req); void i915_scheduler_wakeup(struct drm_device *dev); void i915_scheduler_work_handler(struct work_struct *work); +bool i915_scheduler_is_request_tracked(struct drm_i915_gem_request *req, + bool *completed, bool *busy);#endif /* _I915_SCHEDULER_H_ */diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index 731d20a..5953590 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -11458,7 +11458,8 @@ static void intel_mmio_flip_work_func(struct work_struct *work) WARN_ON(__i915_wait_request(mmio_flip->req, mmio_flip->crtc->reset_counter, false, NULL, - &mmio_flip->i915->rps.mmioflips)); + &mmio_flip->i915->rps.mmioflips, + false)); i915_gem_request_unreference(mmio_flip->req); }@@ -13523,7 +13524,7 @@ static int intel_atomic_prepare_commit(struct drm_device *dev, ret = __i915_wait_request(intel_plane_state->wait_req,reset_counter, true, - NULL, NULL); + NULL, NULL, false);/* Swallow -EIO errors to allow updates during hw lockup. */if (ret == -EIO) diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c index ca7b8af..a2093f5 100644 --- a/drivers/gpu/drm/i915/intel_ringbuffer.c +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c @@ -2304,7 +2304,7 @@ int intel_ring_idle(struct intel_engine_cs *ring) return __i915_wait_request(req, atomic_read(&to_i915(ring->dev)->gpu_error.reset_counter), to_i915(ring->dev)->mm.interruptible, - NULL, NULL); + NULL, NULL, true); }int intel_ring_alloc_request_extras(struct drm_i915_gem_request *request)
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