This is a note to let you know that I've just added the patch titled
ALSA: info: Fix potential deadlock at disconnection
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
alsa-info-fix-potential-deadlock-at-disconnection.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From c7a60651953359f98dbf24b43e1bf561e1573ed4 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@xxxxxxx>
Date: Thu, 9 Nov 2023 15:19:54 +0100
Subject: ALSA: info: Fix potential deadlock at disconnection
From: Takashi Iwai <tiwai@xxxxxxx>
commit c7a60651953359f98dbf24b43e1bf561e1573ed4 upstream.
As reported recently, ALSA core info helper may cause a deadlock at
the forced device disconnection during the procfs operation.
The proc_remove() (that is called from the snd_card_disconnect()
helper) has a synchronization of the pending procfs accesses via
wait_for_completion(). Meanwhile, ALSA procfs helper takes the global
mutex_lock(&info_mutex) at both the proc_open callback and
snd_card_info_disconnect() helper. Since the proc_open can't finish
due to the mutex lock, wait_for_completion() never returns, either,
hence it deadlocks.
TASK#1 TASK#2
proc_reg_open()
takes use_pde()
snd_info_text_entry_open()
snd_card_disconnect()
snd_info_card_disconnect()
takes mutex_lock(&info_mutex)
proc_remove()
wait_for_completion(unused_pde)
... waiting task#1 closes
mutex_lock(&info_mutex)
=> DEADLOCK
This patch is a workaround for avoiding the deadlock scenario above.
The basic strategy is to move proc_remove() call outside the mutex
lock. proc_remove() can work gracefully without extra locking, and it
can delete the tree recursively alone. So, we call proc_remove() at
snd_info_card_disconnection() at first, then delete the rest resources
recursively within the info_mutex lock.
After the change, the function snd_info_disconnect() doesn't do
disconnection by itself any longer, but it merely clears the procfs
pointer. So rename the function to snd_info_clear_entries() for
avoiding confusion.
The similar change is applied to snd_info_free_entry(), too. Since
the proc_remove() is called only conditionally with the non-NULL
entry->p, it's skipped after the snd_info_clear_entries() call.
Reported-by: Shinhyung Kang <s47.kang@xxxxxxxxxxx>
Closes: https://lore.kernel.org/r/664457955.21699345385931.JavaMail.epsvc@epcpadp4
Reviewed-by: Jaroslav Kysela <perex@xxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20231109141954.4283-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
sound/core/info.c | 21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)
--- a/sound/core/info.c
+++ b/sound/core/info.c
@@ -72,7 +72,7 @@ struct snd_info_private_data {
};
static int snd_info_version_init(void);
-static void snd_info_disconnect(struct snd_info_entry *entry);
+static void snd_info_clear_entries(struct snd_info_entry *entry);
/*
@@ -598,11 +598,16 @@ void snd_info_card_disconnect(struct snd
{
if (!card)
return;
- mutex_lock(&info_mutex);
+
proc_remove(card->proc_root_link);
- card->proc_root_link = NULL;
if (card->proc_root)
- snd_info_disconnect(card->proc_root);
+ proc_remove(card->proc_root->p);
+
+ mutex_lock(&info_mutex);
+ if (card->proc_root)
+ snd_info_clear_entries(card->proc_root);
+ card->proc_root_link = NULL;
+ card->proc_root = NULL;
mutex_unlock(&info_mutex);
}
@@ -776,15 +781,14 @@ struct snd_info_entry *snd_info_create_c
}
EXPORT_SYMBOL(snd_info_create_card_entry);
-static void snd_info_disconnect(struct snd_info_entry *entry)
+static void snd_info_clear_entries(struct snd_info_entry *entry)
{
struct snd_info_entry *p;
if (!entry->p)
return;
list_for_each_entry(p, &entry->children, list)
- snd_info_disconnect(p);
- proc_remove(entry->p);
+ snd_info_clear_entries(p);
entry->p = NULL;
}
@@ -801,8 +805,9 @@ void snd_info_free_entry(struct snd_info
if (!entry)
return;
if (entry->p) {
+ proc_remove(entry->p);
mutex_lock(&info_mutex);
- snd_info_disconnect(entry);
+ snd_info_clear_entries(entry);
mutex_unlock(&info_mutex);
}
Patches currently in stable-queue which might be from tiwai@xxxxxxx are
queue-4.14/alsa-info-fix-potential-deadlock-at-disconnection.patch
queue-4.14/alsa-hda-fix-possible-null-ptr-deref-when-assigning-.patch
