From 99e48bf98dd036090b480a12c39e8b971731247e Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Mon, 15 Jan 2018 09:20:41 +0000 Subject: [PATCH] drm/i915: Lock out execlist tasklet while peeking inside for busy-stats In order to prevent a race condition where we may end up overaccounting the active state and leaving the busy-stats believing the GPU is 100% busy, lock out the tasklet while we reconstruct the busy state. There is no direct spinlock guard for the execlists->port[], so we need to utilise tasklet_disable() as a synchronous barrier to prevent it, the only writer to execlists->port[], from running at the same time as the enable. Fixes: 4900727d35bb ("drm/i915/pmu: Reconstruct active state on starting busy-stats") Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20180115092041.13509-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin --- drivers/gpu/drm/i915/intel_engine_cs.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c index d790bdc227ff..b221610f2365 100644 --- a/drivers/gpu/drm/i915/intel_engine_cs.c +++ b/drivers/gpu/drm/i915/intel_engine_cs.c @@ -1943,16 +1943,22 @@ intel_engine_lookup_user(struct drm_i915_private *i915, u8 class, u8 instance) */ int intel_enable_engine_stats(struct intel_engine_cs *engine) { + struct intel_engine_execlists *execlists = &engine->execlists; unsigned long flags; + int err = 0; if (!intel_engine_supports_stats(engine)) return -ENODEV; + tasklet_disable(&execlists->tasklet); spin_lock_irqsave(&engine->stats.lock, flags); - if (engine->stats.enabled == ~0) - goto busy; + + if (unlikely(engine->stats.enabled == ~0)) { + err = -EBUSY; + goto unlock; + } + if (engine->stats.enabled++ == 0) { - struct intel_engine_execlists *execlists = &engine->execlists; const struct execlist_port *port = execlists->port; unsigned int num_ports = execlists_num_ports(execlists); @@ -1967,14 +1973,12 @@ int intel_enable_engine_stats(struct intel_engine_cs *engine) if (engine->stats.active) engine->stats.start = engine->stats.enabled_at; } + +unlock: spin_unlock_irqrestore(&engine->stats.lock, flags); + tasklet_enable(&execlists->tasklet); - return 0; - -busy: - spin_unlock_irqrestore(&engine->stats.lock, flags); - - return -EBUSY; + return err; } static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine)