[PATCH v6 2/2] ASoC: SOF: Fix deadlock when shutdown a frozen userspace

[Ricardo Ribalda]

During kexec(), the userspace is frozen. Therefore we cannot wait for it
to complete.

Avoid running snd_sof_machine_unregister during shutdown.

This fixes:

[   84.943749] Freezing user space processes ... (elapsed 0.111 seconds) done.
[  246.784446] INFO: task kexec-lite:5123 blocked for more than 122 seconds.
[  246.819035] Call Trace:
[  246.821782]  <TASK>
[  246.824186]  __schedule+0x5f9/0x1263
[  246.828231]  schedule+0x87/0xc5
[  246.831779]  snd_card_disconnect_sync+0xb5/0x127
...
[  246.889249]  snd_sof_device_shutdown+0xb4/0x150
[  246.899317]  pci_device_shutdown+0x37/0x61
[  246.903990]  device_shutdown+0x14c/0x1d6
[  246.908391]  kernel_kexec+0x45/0xb9

And:

[  246.893222] INFO: task kexec-lite:4891 blocked for more than 122 seconds.
[  246.927709] Call Trace:
[  246.930461]  <TASK>
[  246.932819]  __schedule+0x5f9/0x1263
[  246.936855]  ? fsnotify_grab_connector+0x5c/0x70
[  246.942045]  schedule+0x87/0xc5
[  246.945567]  schedule_timeout+0x49/0xf3
[  246.949877]  wait_for_completion+0x86/0xe8
[  246.954463]  snd_card_free+0x68/0x89
...
[  247.001080]  platform_device_unregister+0x12/0x35

Cc: stable at vger.kernel.org
Fixes: 83bfc7e793b5 ("ASoC: SOF: core: unregister clients and machine drivers in .shutdown")
Signed-off-by: Ricardo Ribalda <ribalda at chromium.org>
---
 sound/soc/sof/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sound/soc/sof/core.c b/sound/soc/sof/core.c
index 3e6141d03770..4301f347bb90 100644
--- a/sound/soc/sof/core.c
+++ b/sound/soc/sof/core.c
@@ -9,6 +9,7 @@
 //
 
 #include <linux/firmware.h>
+#include <linux/kexec.h>
 #include <linux/module.h>
 #include <sound/soc.h>
 #include <sound/sof.h>
@@ -484,7 +485,8 @@ int snd_sof_device_shutdown(struct device *dev)
 	 * make sure clients and machine driver(s) are unregistered to force
 	 * all userspace devices to be closed prior to the DSP shutdown sequence
 	 */
-	sof_unregister_clients(sdev);
+	if (!kexec_with_frozen_processes())
+		sof_unregister_clients(sdev);
 
 	snd_sof_machine_unregister(sdev, pdata);
 

-- 
2.38.1.584.g0f3c55d4c2-goog-b4-0.11.0-dev-696ae