From patchwork Thu Nov 9 14:19:54 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Takashi Iwai X-Patchwork-Id: 13451185 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04945C4332F for ; Thu, 9 Nov 2023 14:20:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231835AbjKIOUD (ORCPT ); Thu, 9 Nov 2023 09:20:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51742 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231586AbjKIOUC (ORCPT ); Thu, 9 Nov 2023 09:20:02 -0500 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 38361D4A for ; Thu, 9 Nov 2023 06:20:00 -0800 (PST) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id DAD451F8B6; Thu, 9 Nov 2023 14:19:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1699539598; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=zltiq+7lYTQ/5OGKhAtwa87gh+N4HoIjDwaTB72eVFY=; b=hNML6KBVpzsran4koyAfs3VPVa9XeW33piN+0odsi1ZwyGX4zwaeYmCe3juDKiDnuu9hNa y1WgUsG45dMoSFLOClm3oYlii3a2EhP6kbl6d+b5XngdQZr03YXrMDpfqw5Iklihy9TXGE UoPObUDvRiPQqixEwlEM4/wkILKCpzY= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1699539598; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=zltiq+7lYTQ/5OGKhAtwa87gh+N4HoIjDwaTB72eVFY=; b=B+cdoID4e15KofeTrfP1l+HIapvPOK+TiOq6zWVcwOkuJGGGFE/UieFugpCrtjLUQckxnI hffmAHFTfxc/dWDg== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id B80E4138E5; Thu, 9 Nov 2023 14:19:58 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id /cb7K47qTGVcagAAMHmgww (envelope-from ); Thu, 09 Nov 2023 14:19:58 +0000 From: Takashi Iwai To: linux-sound@vger.kernel.org Cc: Shinhyung Kang Subject: [PATCH] ALSA: info: Fix potential deadlock at disconnection Date: Thu, 9 Nov 2023 15:19:54 +0100 Message-Id: <20231109141954.4283-1-tiwai@suse.de> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-sound@vger.kernel.org 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 Closes: https://lore.kernel.org/r/664457955.21699345385931.JavaMail.epsvc@epcpadp4 Signed-off-by: Takashi Iwai Reviewed-by: Jaroslav Kysela --- sound/core/info.c | 21 +++++++++++++-------- 1 file 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); }