linux-kernel - [PATCH] ALSA: core: Fix deadlock when shutdown a frozen userspace

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Message-Id: <20221127-snd-freeze-v1-0-57461a366ec2@chromium.org>
Date:   Sun, 27 Nov 2022 23:30:02 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>
Cc:     Ricardo Ribalda <ribalda@...omium.org>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>
Subject: [PATCH] ALSA: core: Fix deadlock when shutdown a frozen userspace

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

Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
---
To: Jaroslav Kysela <perex@...ex.cz>
To: Takashi Iwai <tiwai@...e.com>
Cc: alsa-devel@...a-project.org
Cc: linux-kernel@...r.kernel.org
Cc: "Joel Fernandes (Google)" <joel@...lfernandes.org>
---
 sound/core/init.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/sound/core/init.c b/sound/core/init.c
index 5377f94eb211..f614a2cdea3d 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 (pm_freezing) {
+		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 (pm_freezing)
+		return 0;
+
 	/* wait, until all devices are ready for the free operation */
 	wait_for_completion(&released);
 

---
base-commit: 4312098baf37ee17a8350725e6e0d0e8590252d4
change-id: 20221127-snd-freeze-1ee143228326

Best regards,
-- 
Ricardo Ribalda <ribalda@...omium.org>