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Subject[PATCH 5.4 175/191] drm/i915/execlists: Fix annotation for decoupling virtual request
Date
From: Chris Wilson <chris@chris-wilson.co.uk>

[ Upstream commit 08ad9a3846fc72b047b110b36d162ffbcf298fa2 ]

As we may signal a request and take the engine->active.lock within the
signaler, the engine submission paths have to use a nested annotation on
their requests -- but we guarantee that we can never submit on the same
engine as the signaling fence.

<4>[ 723.763281] WARNING: possible circular locking dependency detected
<4>[ 723.763285] 5.3.0-g80fa0e042cdb-drmtip_379+ #1 Tainted: G U
<4>[ 723.763288] ------------------------------------------------------
<4>[ 723.763291] gem_exec_await/1388 is trying to acquire lock:
<4>[ 723.763294] ffff93a7b53221d8 (&engine->active.lock){..-.}, at: execlists_submit_request+0x2b/0x1e0 [i915]
<4>[ 723.763378]
but task is already holding lock:
<4>[ 723.763381] ffff93a7c25f6d20 (&i915_request_get(rq)->submit/1){-.-.}, at: __i915_sw_fence_complete+0x1b2/0x250 [i915]
<4>[ 723.763420]
which lock already depends on the new lock.

<4>[ 723.763423]
the existing dependency chain (in reverse order) is:
<4>[ 723.763427]
-> #2 (&i915_request_get(rq)->submit/1){-.-.}:
<4>[ 723.763434] _raw_spin_lock_irqsave_nested+0x39/0x50
<4>[ 723.763478] __i915_sw_fence_complete+0x1b2/0x250 [i915]
<4>[ 723.763513] intel_engine_breadcrumbs_irq+0x3aa/0x5e0 [i915]
<4>[ 723.763600] cs_irq_handler+0x49/0x50 [i915]
<4>[ 723.763659] gen11_gt_irq_handler+0x17b/0x280 [i915]
<4>[ 723.763690] gen11_irq_handler+0x54/0xf0 [i915]
<4>[ 723.763695] __handle_irq_event_percpu+0x41/0x2d0
<4>[ 723.763699] handle_irq_event_percpu+0x2b/0x70
<4>[ 723.763702] handle_irq_event+0x2f/0x50
<4>[ 723.763706] handle_edge_irq+0xee/0x1a0
<4>[ 723.763709] do_IRQ+0x7e/0x160
<4>[ 723.763712] ret_from_intr+0x0/0x1d
<4>[ 723.763717] __slab_alloc.isra.28.constprop.33+0x4f/0x70
<4>[ 723.763720] kmem_cache_alloc+0x28d/0x2f0
<4>[ 723.763724] vm_area_dup+0x15/0x40
<4>[ 723.763727] dup_mm+0x2dd/0x550
<4>[ 723.763730] copy_process+0xf21/0x1ef0
<4>[ 723.763734] _do_fork+0x71/0x670
<4>[ 723.763737] __se_sys_clone+0x6e/0xa0
<4>[ 723.763741] do_syscall_64+0x4f/0x210
<4>[ 723.763744] entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4>[ 723.763747]
-> #1 (&(&rq->lock)->rlock#2){-.-.}:
<4>[ 723.763752] _raw_spin_lock+0x2a/0x40
<4>[ 723.763789] __unwind_incomplete_requests+0x3eb/0x450 [i915]
<4>[ 723.763825] __execlists_submission_tasklet+0x9ec/0x1d60 [i915]
<4>[ 723.763864] execlists_submission_tasklet+0x34/0x50 [i915]
<4>[ 723.763874] tasklet_action_common.isra.5+0x47/0xb0
<4>[ 723.763878] __do_softirq+0xd8/0x4ae
<4>[ 723.763881] irq_exit+0xa9/0xc0
<4>[ 723.763883] smp_apic_timer_interrupt+0xb7/0x280
<4>[ 723.763887] apic_timer_interrupt+0xf/0x20
<4>[ 723.763892] cpuidle_enter_state+0xae/0x450
<4>[ 723.763895] cpuidle_enter+0x24/0x40
<4>[ 723.763899] do_idle+0x1e7/0x250
<4>[ 723.763902] cpu_startup_entry+0x14/0x20
<4>[ 723.763905] start_secondary+0x15f/0x1b0
<4>[ 723.763908] secondary_startup_64+0xa4/0xb0
<4>[ 723.763911]
-> #0 (&engine->active.lock){..-.}:
<4>[ 723.763916] __lock_acquire+0x15d8/0x1ea0
<4>[ 723.763919] lock_acquire+0xa6/0x1c0
<4>[ 723.763922] _raw_spin_lock_irqsave+0x33/0x50
<4>[ 723.763956] execlists_submit_request+0x2b/0x1e0 [i915]
<4>[ 723.764002] submit_notify+0xa8/0x13c [i915]
<4>[ 723.764035] __i915_sw_fence_complete+0x81/0x250 [i915]
<4>[ 723.764054] i915_sw_fence_wake+0x51/0x64 [i915]
<4>[ 723.764054] __i915_sw_fence_complete+0x1ee/0x250 [i915]
<4>[ 723.764054] dma_i915_sw_fence_wake_timer+0x14/0x20 [i915]
<4>[ 723.764054] dma_fence_signal_locked+0x9e/0x1c0
<4>[ 723.764054] dma_fence_signal+0x1f/0x40
<4>[ 723.764054] vgem_fence_signal_ioctl+0x67/0xc0 [vgem]
<4>[ 723.764054] drm_ioctl_kernel+0x83/0xf0
<4>[ 723.764054] drm_ioctl+0x2f3/0x3b0
<4>[ 723.764054] do_vfs_ioctl+0xa0/0x6f0
<4>[ 723.764054] ksys_ioctl+0x35/0x60
<4>[ 723.764054] __x64_sys_ioctl+0x11/0x20
<4>[ 723.764054] do_syscall_64+0x4f/0x210
<4>[ 723.764054] entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4>[ 723.764054]
other info that might help us debug this:

<4>[ 723.764054] Chain exists of:
&engine->active.lock --> &(&rq->lock)->rlock#2 --> &i915_request_get(rq)->submit/1

<4>[ 723.764054] Possible unsafe locking scenario:

<4>[ 723.764054] CPU0 CPU1
<4>[ 723.764054] ---- ----
<4>[ 723.764054] lock(&i915_request_get(rq)->submit/1);
<4>[ 723.764054] lock(&(&rq->lock)->rlock#2);
<4>[ 723.764054] lock(&i915_request_get(rq)->submit/1);
<4>[ 723.764054] lock(&engine->active.lock);
<4>[ 723.764054]
*** DEADLOCK ***

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111862
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004194758.19679-1-chris@chris-wilson.co.uk
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/i915/gt/intel_lrc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 06a506c29463..d564bfcab6a3 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -525,7 +525,8 @@ __unwind_incomplete_requests(struct intel_engine_cs *engine)
*/
if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
&rq->fence.flags)) {
- spin_lock(&rq->lock);
+ spin_lock_nested(&rq->lock,
+ SINGLE_DEPTH_NESTING);
i915_request_cancel_breadcrumb(rq);
spin_unlock(&rq->lock);
}
--
2.20.1


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