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authorTakashi Iwai <tiwai@suse.de>2023-11-09 15:19:54 +0100
committerTakashi Iwai <tiwai@suse.de>2023-11-09 16:06:33 +0100
commitc7a60651953359f98dbf24b43e1bf561e1573ed4 (patch)
treeb9916a763f9d3ba447bce0662f629dcec814b63a /sound
parent3e3ab468ebdfd79fb2c80f381b70b3815801988e (diff)
ALSA: info: Fix potential deadlock at disconnection
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@samsung.com> Closes: https://lore.kernel.org/r/664457955.21699345385931.JavaMail.epsvc@epcpadp4 Reviewed-by: Jaroslav Kysela <perex@perex.cz> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/20231109141954.4283-1-tiwai@suse.de Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound')
-rw-r--r--sound/core/info.c21
1 files changed, 13 insertions, 8 deletions
diff --git a/sound/core/info.c b/sound/core/info.c
index 0b2f04dcb589..e2f302e55bbb 100644
--- a/sound/core/info.c
+++ b/sound/core/info.c
@@ -56,7 +56,7 @@ 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);
/*
@@ -569,11 +569,16 @@ void snd_info_card_disconnect(struct snd_card *card)
{
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);
}
@@ -745,15 +750,14 @@ struct snd_info_entry *snd_info_create_card_entry(struct snd_card *card,
}
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;
}
@@ -770,8 +774,9 @@ void snd_info_free_entry(struct snd_info_entry * entry)
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);
}