4.19-stable review patch. If anyone has any objections, please let me know.
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From: Takashi Iwai tiwai@suse.de
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@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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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); }