From 74c7b0782b15bc2478f557cea34b3fe34d452dc6 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 8 Dec 2017 12:10:33 +0000 Subject: [PATCH] drm/i915: Stop listening to request resubmission from the signaler kthread Mime-version: 1.0 Content-type: text/plain; charset=UTF-8 Content-transfer-encoding: 8bit Git-commit: 74c7b0782b15bc2478f557cea34b3fe34d452dc6 Patch-mainline: v4.15-rc5 References: FATE#322643 bsc#1055900 No-fix: 776bc27fd8ab67a675cb0041d3af361af5d0e290 The intent here was that we would be listening to i915_gem_request_unsubmit in order to cancel the signaler quickly and release the reference on the request. Cancelling the signaler is done directly via intel_engine_cancel_signaling (called from unsubmit), but that does not directly wake up the signaling thread, and neither does setting the request->global_seqno back to zero wake up listeners to the request->execute waitqueue. So the only time that listening to the request->execute waitqueue would wake up the signaling kthread would be on the request resubmission, during which time we would already receive wake ups from rejoining the global breadcrumbs wait rbtree. Trying to wake up to release the request remains an issue. If the signaling was cancelled and no other request required signaling, then it is possible for us to shutdown with the reference on the request still held. To ensure that we do not try to shutdown, leaking that request, we kick the signaling threads whenever we disarm the breadcrumbs, i.e. on parking the engine when idle. V2: We do need to be sure to release the last reference on stopping the kthread; asserting that it has been dropped already is insufficient. Fixes: d6a2289d9d6b ("drm/i915: Remove the preempted request from the execution queue") Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Cc: Michał Winiarski Link: https://patchwork.freedesktop.org/patch/msgid/20171208121033.5236-1-chris@chris-wilson.co.uk Acked-by: Daniel Vetter Reviewed-by: Tvrtko Ursulin (cherry picked from commit 776bc27fd8ab67a675cb0041d3af361af5d0e290) Signed-off-by: Jani Nikula Acked-by: Takashi Iwai --- drivers/gpu/drm/i915/intel_breadcrumbs.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) --- a/drivers/gpu/drm/i915/intel_breadcrumbs.c +++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c @@ -186,7 +186,7 @@ void intel_engine_disarm_breadcrumbs(str struct intel_wait *wait, *n, *first; if (!b->irq_armed) - return; + goto wakeup_signaler; /* We only disarm the irq when we are idle (all requests completed), * so if the bottom-half remains asleep, it missed the request @@ -208,6 +208,14 @@ void intel_engine_disarm_breadcrumbs(str b->waiters = RB_ROOT; spin_unlock_irq(&b->rb_lock); + + /* + * The signaling thread may be asleep holding a reference to a request, + * that had its signaling cancelled prior to being preempted. We need + * to kick the signaler, just in case, to release any such reference. + */ +wakeup_signaler: + wake_up_process(b->signaler); } static bool use_fake_irq(const struct intel_breadcrumbs *b) @@ -651,23 +659,15 @@ static int intel_breadcrumbs_signaler(vo } if (unlikely(do_schedule)) { - DEFINE_WAIT(exec); - if (kthread_should_park()) kthread_parkme(); - if (kthread_should_stop()) { - GEM_BUG_ON(request); + if (unlikely(kthread_should_stop())) { + i915_gem_request_put(request); break; } - if (request) - add_wait_queue(&request->execute, &exec); - schedule(); - - if (request) - remove_wait_queue(&request->execute, &exec); } i915_gem_request_put(request); } while (1);