Virtual engines are fleeting. They carry a reference count and may be freed
when their last request is retired. This makes them unsuitable for the
task of housing engine->retire.work so assert that it is not used.
Tvrtko tracked down an instance where we did indeed violate this rule.
In virtual_submit_request, we flush a completed request directly with
__i915_request_submit and this causes us to queue that request on the
veng's breadcrumb list and signal it. Leading us down a path where we
should not attach the retire.
Reported-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: dc93c9b693 ("drm/i915/gt: Schedule request retirement when signaler idles")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200206204915.2636606-1-chris@chris-wilson.co.uk
(cherry picked from commit f91d8156ab)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
The function intel_engine_breadcrumbs_irq() is always invoked from an interrupt
handler and for that reason it invokes (as an optimisation) only spin_lock()
for locking assuming that the interrupts are already disabled. The
function intel_engine_signal_breadcrumbs() is provided to disable
interrupts while the former function is invoked so that assumption is
also true for callers from preemptible context.
On PREEMPT_RT local_irq_disable() really disables interrupts and this
forbids to invoke spin_lock() which becomes a sleeping spinlock.
This is also problematic with `threadirqs' in conjunction with
irq_work. With force threading the interrupt handler, the handler is
invoked with disabled BH but with interrupts enabled. This is okay and
the lock itself is never acquired in IRQ context. This changes with
irq_work (signal_irq_work()) which _still_ invokes
intel_engine_breadcrumbs_irq() from IRQ context. Lockdep should see this
and complain.
Acquire the locks in intel_engine_breadcrumbs_irq() with _irqsave()
suffix and let all callers invoke intel_engine_breadcrumbs_irq()
directly instead using intel_engine_signal_breadcrumbs().
Reported-by: Clark Williams <williams@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190926105644.16703-2-bigeasy@linutronix.de
The lockdep_assert_irqs_disabled() check is needless. The previous
lockdep_assert_held() check ensures that the lock is acquired and while
the lock is acquired lockdep also prints a warning if the interrupts are
not disabled if they have to be.
These IRQ-off asserts trigger on PREEMPT_RT because the locks become
sleeping locks and do not really disable interrupts.
Remove lockdep_assert_irqs_disabled().
Reported-by: Clark Williams <williams@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190926105644.16703-3-bigeasy@linutronix.de
We need the rename of reservation_object to dma_resv.
The solution on this merge came from linux-next:
From: Stephen Rothwell <sfr@canb.auug.org.au>
Date: Wed, 14 Aug 2019 12:48:39 +1000
Subject: [PATCH] drm: fix up fallout from "dma-buf: rename reservation_object to dma_resv"
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
---
drivers/gpu/drm/i915/gt/intel_engine_pool.c | 8 ++++----
3 files changed, 7 insertions(+), 7 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pool.c b/drivers/gpu/drm/i915/gt/intel_engine_pool.c
index 03d90b49584a..4cd54c569911 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_pool.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_pool.c
@@ -43,12 +43,12 @@ static int pool_active(struct i915_active *ref)
{
struct intel_engine_pool_node *node =
container_of(ref, typeof(*node), active);
- struct reservation_object *resv = node->obj->base.resv;
+ struct dma_resv *resv = node->obj->base.resv;
int err;
- if (reservation_object_trylock(resv)) {
- reservation_object_add_excl_fence(resv, NULL);
- reservation_object_unlock(resv);
+ if (dma_resv_trylock(resv)) {
+ dma_resv_add_excl_fence(resv, NULL);
+ dma_resv_unlock(resv);
}
err = i915_gem_object_pin_pages(node->obj);
which is a simplified version from a previous one which had:
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
The timestamp and the cb_list are mutually exclusive, the cb_list can
only be added to prior to being signaled (and once signaled we drain),
while the timestamp is only valid upon being signaled. Both the
timestamp and the cb_list are only valid while the fence is alive, and
as soon as no references are held can be replaced by the rcu_head.
By reusing the union for the timestamp, we squeeze the base dma_fence
struct to 64 bytes on x86-64.
v2: Sort the union chronologically
Suggested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Christian König <christian.koenig@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>.
Link: https://patchwork.freedesktop.org/patch/msgid/20190817153022.5749-1-chris@chris-wilson.co.uk
Currently there is an underlying assumption that i915_request_unsubmit()
is synchronous wrt the GPU -- that is the request is no longer in flight
as we remove it. In the near future that may change, and this may upset
our signaling as we can process an interrupt for that request while it
is no longer in flight.
CPU0 CPU1
intel_engine_breadcrumbs_irq
(queue request completion)
i915_request_cancel_signaling
... ...
i915_request_enable_signaling
dma_fence_signal
Hence in the time it took us to drop the lock to signal the request, a
preemption event may have occurred and re-queued the request. In the
process, that request would have seen I915_FENCE_FLAG_SIGNAL clear and
so reused the rq->signal_link that was in use on CPU0, leading to bad
pointer chasing in intel_engine_breadcrumbs_irq.
A related issue was that if someone started listening for a signal on a
completed but no longer in-flight request, we missed the opportunity to
immediately signal that request.
Furthermore, as intel_contexts may be immediately released during
request retirement, in order to be entirely sure that
intel_engine_breadcrumbs_irq may no longer dereference the intel_context
(ce->signals and ce->signal_link), we must wait for irq spinlock.
In order to prevent the race, we use a bit in the fence.flags to signal
the transfer onto the signal list inside intel_engine_breadcrumbs_irq.
For simplicity, we use the DMA_FENCE_FLAG_SIGNALED_BIT as it then
quickly signals to any outside observer that the fence is indeed signaled.
v2: Sketch out potential dma-fence API for manual signaling
v3: And the test_and_set_bit()
Fixes: 52c0fdb25c ("drm/i915: Replace global breadcrumbs with per-context interrupt tracking")
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: https://patchwork.freedesktop.org/patch/msgid/20190508112452.18942-1-chris@chris-wilson.co.uk
