From mboxrd@z Thu Jan 1 00:00:00 1970 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 65BEDC6379F for ; Thu, 9 Feb 2023 23:57:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229891AbjBIX5Z (ORCPT ); Thu, 9 Feb 2023 18:57:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35784 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229881AbjBIX5Y (ORCPT ); Thu, 9 Feb 2023 18:57:24 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8060A552A8; Thu, 9 Feb 2023 15:57:22 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 1D647B8237D; Thu, 9 Feb 2023 23:57:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B2C96C433EF; Thu, 9 Feb 2023 23:57:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1675987039; bh=EimtB5JKds8OUJCRIIr9unO8IjKs+/HwWrMpSoPhw6k=; h=Date:To:From:Subject:From; b=dyZbB/hEwuGwONGE5nMooacWFBoxhfox1YxfOhSrWGgKk+LqZtblzzZWL6UR+RlH5 +VIgnrFlEp5UdXggSTSxxEUl5OhhxjDizOgEO9St8awZOt4llPGdOBKTL5Gh7dyK6z Bcy7uufcA/6HSrjRzY2QmR9hMze2B1tX1NK5W4Bs= Date: Thu, 09 Feb 2023 15:57:19 -0800 To: mm-commits@vger.kernel.org, stable@vger.kernel.org, songmuchun@bytedance.com, roman.gushchin@linux.dev, kent.overstreet@gmail.com, zhengqi.arch@bytedance.com, akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] mm-shrinkers-fix-deadlock-in-shrinker-debugfs.patch removed from -mm tree Message-Id: <20230209235719.B2C96C433EF@smtp.kernel.org> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The quilt patch titled Subject: mm: shrinkers: fix deadlock in shrinker debugfs has been removed from the -mm tree. Its filename was mm-shrinkers-fix-deadlock-in-shrinker-debugfs.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Qi Zheng Subject: mm: shrinkers: fix deadlock in shrinker debugfs Date: Thu, 2 Feb 2023 18:56:12 +0800 The debugfs_remove_recursive() is invoked by unregister_shrinker(), which is holding the write lock of shrinker_rwsem. It will waits for the handler of debugfs file complete. The handler also needs to hold the read lock of shrinker_rwsem to do something. So it may cause the following deadlock: CPU0 CPU1 debugfs_file_get() shrinker_debugfs_count_show()/shrinker_debugfs_scan_write() unregister_shrinker() --> down_write(&shrinker_rwsem); debugfs_remove_recursive() // wait for (A) --> wait_for_completion(); // wait for (B) --> down_read_killable(&shrinker_rwsem) debugfs_file_put() -- (A) up_write() -- (B) The down_read_killable() can be killed, so that the above deadlock can be recovered. But it still requires an extra kill action, otherwise it will block all subsequent shrinker-related operations, so it's better to fix it. [akpm@linux-foundation.org: fix CONFIG_SHRINKER_DEBUG=n stub] Link: https://lkml.kernel.org/r/20230202105612.64641-1-zhengqi.arch@bytedance.com Fixes: 5035ebc644ae ("mm: shrinkers: introduce debugfs interface for memory shrinkers") Signed-off-by: Qi Zheng Reviewed-by: Roman Gushchin Cc: Kent Overstreet Cc: Muchun Song Cc: Signed-off-by: Andrew Morton --- include/linux/shrinker.h | 5 +++-- mm/shrinker_debug.c | 13 ++++++++----- mm/vmscan.c | 6 +++++- 3 files changed, 16 insertions(+), 8 deletions(-) --- a/include/linux/shrinker.h~mm-shrinkers-fix-deadlock-in-shrinker-debugfs +++ a/include/linux/shrinker.h @@ -107,7 +107,7 @@ extern void synchronize_shrinkers(void); #ifdef CONFIG_SHRINKER_DEBUG extern int shrinker_debugfs_add(struct shrinker *shrinker); -extern void shrinker_debugfs_remove(struct shrinker *shrinker); +extern struct dentry *shrinker_debugfs_remove(struct shrinker *shrinker); extern int __printf(2, 3) shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...); #else /* CONFIG_SHRINKER_DEBUG */ @@ -115,8 +115,9 @@ static inline int shrinker_debugfs_add(s { return 0; } -static inline void shrinker_debugfs_remove(struct shrinker *shrinker) +static inline struct dentry *shrinker_debugfs_remove(struct shrinker *shrinker) { + return NULL; } static inline __printf(2, 3) int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...) --- a/mm/shrinker_debug.c~mm-shrinkers-fix-deadlock-in-shrinker-debugfs +++ a/mm/shrinker_debug.c @@ -246,18 +246,21 @@ int shrinker_debugfs_rename(struct shrin } EXPORT_SYMBOL(shrinker_debugfs_rename); -void shrinker_debugfs_remove(struct shrinker *shrinker) +struct dentry *shrinker_debugfs_remove(struct shrinker *shrinker) { + struct dentry *entry = shrinker->debugfs_entry; + lockdep_assert_held(&shrinker_rwsem); kfree_const(shrinker->name); shrinker->name = NULL; - if (!shrinker->debugfs_entry) - return; + if (entry) { + ida_free(&shrinker_debugfs_ida, shrinker->debugfs_id); + shrinker->debugfs_entry = NULL; + } - debugfs_remove_recursive(shrinker->debugfs_entry); - ida_free(&shrinker_debugfs_ida, shrinker->debugfs_id); + return entry; } static int __init shrinker_debugfs_init(void) --- a/mm/vmscan.c~mm-shrinkers-fix-deadlock-in-shrinker-debugfs +++ a/mm/vmscan.c @@ -741,6 +741,8 @@ EXPORT_SYMBOL(register_shrinker); */ void unregister_shrinker(struct shrinker *shrinker) { + struct dentry *debugfs_entry; + if (!(shrinker->flags & SHRINKER_REGISTERED)) return; @@ -749,9 +751,11 @@ void unregister_shrinker(struct shrinker shrinker->flags &= ~SHRINKER_REGISTERED; if (shrinker->flags & SHRINKER_MEMCG_AWARE) unregister_memcg_shrinker(shrinker); - shrinker_debugfs_remove(shrinker); + debugfs_entry = shrinker_debugfs_remove(shrinker); up_write(&shrinker_rwsem); + debugfs_remove_recursive(debugfs_entry); + kfree(shrinker->nr_deferred); shrinker->nr_deferred = NULL; } _ Patches currently in -mm which might be from zhengqi.arch@bytedance.com are