[PATCH v3 2/2] ALSA: core: Fix deadlock when shutdown a frozen userspace

From: Ricardo Ribalda
Date: Mon Nov 28 2022 - 04:10:50 EST


If the user space is frozen, we cannot wait for it to complete.

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

Fixes: 83bfc7e793b5 ("ASoC: SOF: core: unregister clients and machine drivers in .shutdown")
Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
sound/core/init.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/sound/core/init.c b/sound/core/init.c
index 5377f94eb211..bc038b49d4d3 100644
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -9,6 +9,7 @@
#include <linux/module.h>
#include <linux/device.h>
#include <linux/file.h>
+#include <linux/freezer.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/ctype.h>
@@ -573,6 +574,11 @@ void snd_card_disconnect_sync(struct snd_card *card)
return;
}

+ if (processes_frozen()) {
+ dev_err(card->dev, "Userspace is frozen, skipping sync\n");
+ return;
+ }
+
spin_lock_irq(&card->files_lock);
wait_event_lock_irq(card->remove_sleep,
list_empty(&card->files_list),
@@ -658,6 +664,13 @@ int snd_card_free(struct snd_card *card)
ret = snd_card_free_when_closed(card);
if (ret)
return ret;
+
+ /*
+ * If userspace is frozen the wait from completion will never end.
+ */
+ if (processes_frozen())
+ return 0;
+
/* wait, until all devices are ready for the free operation */
wait_for_completion(&released);


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