[PATCH v3] drm/xe/devcoredump: Defer devcoredump initialization during probe

[Balasubramani Vivekanandan]

Doing devcoredump initializing before GT though look harmless, it leads
to problem during driver unbind. Because of this order, GT/Engine
release functions will be called before xe devcoredump release function
(xe_driver_devcoredump_fini) leading to the following kernel crash[1]
because the devcoredump functions might still use GT/Engine
datastructures after those are freed.

The following crash is observed while running the IGT
xe_wedged at wedged-at-any-timeout. The test forces a wedged state by
submitting a worload which hangs. Then does a unbind/rebind of the
driver to recover from the wedged state.
The hanged worload leads to a devcoredump. The following crash is
noticed when the devcoredump capture races with the driver unbind.
During driver unbind, the release function hw_engine_fini() will be
called which assigns NULL to hwe->gt. But the same data structure is
accessed during the coredump capture in the function
xe_engine_snapshot_print by reading snapshot->hwe->gt.

With this patch, we make sure the devcoredump is stopped before
deinitializing the core driver functions.

[1]:
BUG: kernel NULL pointer dereference, address: 0000000000000000
Workqueue: events_unbound xe_devcoredump_deferred_snap_work [xe]
RIP: 0010:xe_engine_snapshot_print+0x47/0x420 [xe]
Call Trace:
 <TASK>
 ? drm_printf+0x64/0x90
 __xe_devcoredump_read+0x23f/0x2d0 [xe]
 ? __pfx___drm_printfn_coredump+0x10/0x10
 ? __pfx___drm_puts_coredump+0x10/0x10
 xe_devcoredump_deferred_snap_work+0x17a/0x190 [xe]
 process_one_work+0x22e/0x6f0
 worker_thread+0x1e8/0x3d0
 ? __pfx_worker_thread+0x10/0x10
 kthread+0x11f/0x250
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x47/0x70
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1a/0x30

v2: Detailed commit description (Rodrigo)
v3: FIXME added (Rodrigo, Stuart)

Fixes: 4209d635a823 ("drm/xe: Remove devcoredump during driver release")
Signed-off-by: Balasubramani Vivekanandan <balasubramani.vivekanandan at intel.com>
---
 drivers/gpu/drm/xe/xe_device.c      | 8 ++++----
 drivers/gpu/drm/xe/xe_guc_capture.c | 6 ++++++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index d04a0ae018e6..ae48cd3c7bf0 100644
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -821,10 +821,6 @@ int xe_device_probe(struct xe_device *xe)
 			return err;
 	}
 
-	err = xe_devcoredump_init(xe);
-	if (err)
-		return err;
-
 	/*
 	 * From here on, if a step fails, make sure a Driver-FLR is triggereed
 	 */
@@ -889,6 +885,10 @@ int xe_device_probe(struct xe_device *xe)
 	    XE_WA(xe->tiles->media_gt, 15015404425_disable))
 		XE_DEVICE_WA_DISABLE(xe, 15015404425);
 
+	err = xe_devcoredump_init(xe);
+	if (err)
+		return err;
+
 	xe_nvm_init(xe);
 
 	err = xe_heci_gsc_init(xe);
diff --git a/drivers/gpu/drm/xe/xe_guc_capture.c b/drivers/gpu/drm/xe/xe_guc_capture.c
index 859a3ba91be5..243dad3e2418 100644
--- a/drivers/gpu/drm/xe/xe_guc_capture.c
+++ b/drivers/gpu/drm/xe/xe_guc_capture.c
@@ -1817,6 +1817,12 @@ void xe_engine_snapshot_print(struct xe_hw_engine_snapshot *snapshot, struct drm
 		   str_yes_no(snapshot->kernel_reserved));
 
 	for (type = GUC_STATE_CAPTURE_TYPE_GLOBAL; type < GUC_STATE_CAPTURE_TYPE_MAX; type++) {
+		/*
+		 * FIXME: During devcoredump print we should avoid accessing the
+		 * driver pointers for gt or engine. Printing should be done only
+		 * using the snapshot captured. Here we are accessing the gt
+		 * pointer. It should be fixed.
+		 */
 		list = xe_guc_capture_get_reg_desc_list(gt, GUC_CAPTURE_LIST_INDEX_PF, type,
 							capture_class, false);
 		snapshot_print_by_list_order(snapshot, p, type, list);
-- 
2.34.1