From 99e48bf98dd036090b480a12c39e8b971731247e Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
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 <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180115092041.13509-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
drivers/gpu/drm/i915/intel_engine_cs.c | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index d790bdc227ffb..b221610f2365f 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;
}
- spin_unlock_irqrestore(&engine->stats.lock, flags);
- return 0;
-
-busy:
+unlock:
spin_unlock_irqrestore(&engine->stats.lock, flags);
+ tasklet_enable(&execlists->tasklet);
- return -EBUSY;
+ return err;
}
static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine)