drm/i915: Don't touch fence->error when resetting an innocent request

If the request has been completed before the reset took effect, we don't
need to mark it up as being a victim. Touching fence->error after the
fence has been signaled is detected by dma_fence_set_error() and
triggers a BUG:

[  231.743133] kernel BUG at ./include/linux/dma-fence.h:434!
[  231.743156] invalid opcode: 0000 [#1] SMP KASAN
[  231.743172] Modules linked in: i915 drm_kms_helper drm iptable_nat nf_nat_ipv4 nf_nat x86_pkg_temp_thermal iosf_mbi i2c_algo_bit cfbfillrect syscopyarea cfbimgblt sysfillrect sysimgblt fb_sys_fops cfbcopyarea fb font fbdev [last unloaded: drm]
[  231.743221] CPU: 2 PID: 20 Comm: kworker/2:0 Tainted: G     U          4.13.0-rc1+ #52
[  231.743236] Hardware name: Hewlett-Packard HP EliteBook 8460p/161C, BIOS 68SCF Ver. F.01 03/11/2011
[  231.743363] Workqueue: events_long i915_hangcheck_elapsed [i915]
[  231.743382] task: ffff8801f42e9780 task.stack: ffff8801f42f8000
[  231.743489] RIP: 0010:i915_gem_reset_engine+0x45a/0x460 [i915]
[  231.743505] RSP: 0018:ffff8801f42ff770 EFLAGS: 00010202
[  231.743521] RAX: 0000000000000007 RBX: ffff8801bf6b1880 RCX: ffffffffa02881a6
[  231.743537] RDX: dffffc0000000000 RSI: dffffc0000000000 RDI: ffff8801bf6b18c8
[  231.743551] RBP: ffff8801f42ff7c8 R08: 0000000000000001 R09: 0000000000000000
[  231.743566] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801edb02d00
[  231.743581] R13: ffff8801e19d4200 R14: 000000000000001d R15: ffff8801ce2a4000
[  231.743599] FS:  0000000000000000(0000) GS:ffff8801f5a80000(0000) knlGS:0000000000000000
[  231.743614] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  231.743629] CR2: 00007f0ebd1add10 CR3: 0000000002621000 CR4: 00000000000406e0
[  231.743643] Call Trace:
[  231.743752]  i915_gem_reset+0x6c/0x150 [i915]
[  231.743853]  i915_reset+0x175/0x210 [i915]
[  231.743958]  i915_reset_device+0x33b/0x350 [i915]
[  231.744061]  ? valleyview_pipestat_irq_handler+0xe0/0xe0 [i915]
[  231.744081]  ? trace_hardirqs_off_caller+0x70/0x110
[  231.744102]  ? _raw_spin_unlock_irqrestore+0x46/0x50
[  231.744120]  ? find_held_lock+0x119/0x150
[  231.744138]  ? mark_lock+0x6d/0x850
[  231.744241]  ? gen8_gt_irq_ack+0x1f0/0x1f0 [i915]
[  231.744262]  ? work_on_cpu_safe+0x60/0x60
[  231.744284]  ? rcu_read_lock_sched_held+0x57/0xa0
[  231.744400]  ? gen6_read32+0x2ba/0x320 [i915]
[  231.744506]  i915_handle_error+0x382/0x5f0 [i915]
[  231.744611]  ? gen6_rps_reset_ei+0x20/0x20 [i915]
[  231.744630]  ? vsnprintf+0x128/0x8e0
[  231.744649]  ? pointer+0x6b0/0x6b0
[  231.744667]  ? debug_check_no_locks_freed+0x1a0/0x1a0
[  231.744688]  ? scnprintf+0x92/0xe0
[  231.744706]  ? snprintf+0xb0/0xb0
[  231.744820]  hangcheck_declare_hang+0x15a/0x1a0 [i915]
[  231.744932]  ? engine_stuck+0x440/0x440 [i915]
[  231.744951]  ? rcu_read_lock_sched_held+0x57/0xa0
[  231.745062]  ? gen6_read32+0x2ba/0x320 [i915]
[  231.745173]  ? gen6_read16+0x320/0x320 [i915]
[  231.745284]  ? intel_engine_get_active_head+0x91/0x170 [i915]
[  231.745401]  i915_hangcheck_elapsed+0x3d8/0x400 [i915]
[  231.745424]  process_one_work+0x3e8/0xac0
[  231.745444]  ? pwq_dec_nr_in_flight+0x110/0x110
[  231.745464]  ? do_raw_spin_lock+0x8e/0x120
[  231.745484]  worker_thread+0x8d/0x720
[  231.745506]  kthread+0x19e/0x1f0
[  231.745524]  ? process_one_work+0xac0/0xac0
[  231.745541]  ? kthread_create_on_node+0xa0/0xa0
[  231.745560]  ret_from_fork+0x27/0x40
[  231.745581] Code: 8b 7d c8 e8 49 0d 02 e1 49 8b 7f 38 48 8b 75 b8 48 83 c7 10 e8 b8 89 be e1 e9 95 fc ff ff 4c 89 e7 e8 4b b9 ff ff e9 30 ff ff ff <0f> 0b 0f 1f 40 00 55 48 89 e5 41 57 41 56 41 55 41 54 49 89 fe
[  231.745767] RIP: i915_gem_reset_engine+0x45a/0x460 [i915] RSP: ffff8801f42ff770

At first glance this looks to be related to commit c64992e035d7
("drm/i915: Look for active requests earlier in the reset path"), but it
could easily happen before as well. On the other hand, we no longer
logged victims due to the active_request being dropped earlier.

v2: Be trickier to unwind the incomplete request as we cannot rely on
request retirement for the lockless per-engine reset.
v3: Reprobe the active request at the time of the reset.

Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Fixes: c64992e035d7 ("drm/i915: Look for active requests earlier in the reset path")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170721123238.16428-15-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> #v1
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -2854,11 +2854,9 @@ i915_gem_reset_prepare_engine(struct intel_engine_cs *engine)
 	if (engine->irq_seqno_barrier)
 		engine->irq_seqno_barrier(engine);
 
-	if (engine_stalled(engine)) {
-		request = i915_gem_find_active_request(engine);
-		if (request && request->fence.error == -EIO)
-			request = ERR_PTR(-EIO); /* Previous reset failed! */
-	}
+	request = i915_gem_find_active_request(engine);
+	if (request && request->fence.error == -EIO)
+		request = ERR_PTR(-EIO); /* Previous reset failed! */
 
 	return request;
 }
@@ -2927,12 +2925,11 @@ static void engine_skip_context(struct drm_i915_gem_request *request)
 	spin_unlock_irqrestore(&engine->timeline->lock, flags);
 }
 
-/* Returns true if the request was guilty of hang */
-static bool i915_gem_reset_request(struct drm_i915_gem_request *request)
+/* Returns the request if it was guilty of the hang */
+static struct drm_i915_gem_request *
+i915_gem_reset_request(struct intel_engine_cs *engine,
+		       struct drm_i915_gem_request *request)
 {
-	/* Read once and return the resolution */
-	const bool guilty = !i915_gem_request_completed(request);
-
 	/* The guilty request will get skipped on a hung engine.
 	 *
 	 * Users of client default contexts do not rely on logical
@@ -2954,15 +2951,34 @@ static bool i915_gem_reset_request(struct drm_i915_gem_request *request)
 	 * subsequent hangs.
 	 */
 
-	if (guilty) {
+	if (engine_stalled(engine)) {
 		i915_gem_context_mark_guilty(request->ctx);
 		skip_request(request);
+
+		/* If this context is now banned, skip all pending requests. */
+		if (i915_gem_context_is_banned(request->ctx))
+			engine_skip_context(request);
 	} else {
-		i915_gem_context_mark_innocent(request->ctx);
-		dma_fence_set_error(&request->fence, -EAGAIN);
+		/*
+		 * Since this is not the hung engine, it may have advanced
+		 * since the hang declaration. Double check by refinding
+		 * the active request at the time of the reset.
+		 */
+		request = i915_gem_find_active_request(engine);
+		if (request) {
+			i915_gem_context_mark_innocent(request->ctx);
+			dma_fence_set_error(&request->fence, -EAGAIN);
+
+			/* Rewind the engine to replay the incomplete rq */
+			spin_lock_irq(&engine->timeline->lock);
+			request = list_prev_entry(request, link);
+			if (&request->link == &engine->timeline->requests)
+				request = NULL;
+			spin_unlock_irq(&engine->timeline->lock);
+		}
 	}
 
-	return guilty;
+	return request;
 }
 
 void i915_gem_reset_engine(struct intel_engine_cs *engine,
@@ -2970,13 +2986,12 @@ void i915_gem_reset_engine(struct intel_engine_cs *engine,
 {
 	engine->irq_posted = 0;
 
-	if (request && i915_gem_reset_request(request)) {
+	if (request)
+		request = i915_gem_reset_request(engine, request);
+
+	if (request) {
 		DRM_DEBUG_DRIVER("resetting %s to restart from tail of request 0x%x\n",
 				 engine->name, request->global_seqno);
-
-		/* If this context is now banned, skip all pending requests. */
-		if (i915_gem_context_is_banned(request->ctx))
-			engine_skip_context(request);
 	}
 
 	/* Setup the CS to resume from the breadcrumb of the hung request */