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drm/i915: Always double check for a missed interrupt for new bottom halves

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After assigning ourselves as the new bottom-half, we must perform a
cursory check to prevent a missed interrupt.  Either we miss the interrupt
whilst programming the hardware, or if there was a previous waiter (for
a later seqno) they may be woken instead of us (due to the inherent race
in the unlocked read of b->tasklet in the irq handler) and so we miss the
wake up.

Spotted-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96806
Fixes: 688e6c7258 ("drm/i915: Slaughter the thundering... herd")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1467805142-22219-1-git-send-email-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2016-07-06 12:39:00 +01:00
parent 91c8a326a1
commit 04171313cb
1 changed files with 11 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
drivers/gpu/drm/i915/intel_breadcrumbs.c
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@ -65,7 +65,7 @@ static void irq_disable(struct intel_engine_cs *engine)
engine->irq_posted = false;
}
static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
static void __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
{
struct intel_engine_cs *engine =
container_of(b, struct intel_engine_cs, breadcrumbs);
@ -73,7 +73,7 @@ static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
assert_spin_locked(&b->lock);
if (b->rpm_wakelock)
return false;
return;
/* Since we are waiting on a request, the GPU should be busy
* and should have its own rpm reference. For completeness,
@ -93,8 +93,6 @@ static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
if (!b->irq_enabled ||
test_bit(engine->id, &i915->gpu_error.missed_irq_rings))
mod_timer(&b->fake_irq, jiffies + 1);
return engine->irq_posted;
}
static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
@ -233,7 +231,15 @@ static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
GEM_BUG_ON(rb_first(&b->waiters) != &wait->node);
b->first_wait = wait;
smp_store_mb(b->tasklet, wait->tsk);
first = __intel_breadcrumbs_enable_irq(b);
/* After assigning ourselves as the new bottom-half, we must
* perform a cursory check to prevent a missed interrupt.
* Either we miss the interrupt whilst programming the hardware,
* or if there was a previous waiter (for a later seqno) they
* may be woken instead of us (due to the inherent race
* in the unlocked read of b->tasklet in the irq handler) and
* so we miss the wake up.
*/
__intel_breadcrumbs_enable_irq(b);
}
GEM_BUG_ON(!b->tasklet);
GEM_BUG_ON(!b->first_wait);