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 03217C636CC for ; Mon, 20 Feb 2023 13:59:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232729AbjBTN7Z (ORCPT ); Mon, 20 Feb 2023 08:59:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51110 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232766AbjBTN7Q (ORCPT ); Mon, 20 Feb 2023 08:59:16 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B50741EFE5 for ; Mon, 20 Feb 2023 05:58:57 -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 04087B80D4F for ; Mon, 20 Feb 2023 13:58:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C165C433EF; Mon, 20 Feb 2023 13:58:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1676901512; bh=dKm4+i288vmyET0T/ytqj+p+gKmXN7S4Rb6+w17rqVo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YYKDa7tS9uqVYaB6WDWfnUyKK24Zh8vX60ID36uoji6aSkgw3V1935OOAQB+9bHmA iAZNTGc1MzsotCkyEqZ8CKlzPQJ5ihJMgW6rnwEB0zf4NdfMJ4sFfecvvdOvMpmof8 V9MnY11aLnEj7dHLBj3C+A9ko+4WhdrE8MFvuz4U= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Qi Zheng , Roman Gushchin , Kent Overstreet , Muchun Song , Andrew Morton Subject: [PATCH 6.1 046/118] mm: shrinkers: fix deadlock in shrinker debugfs Date: Mon, 20 Feb 2023 14:36:02 +0100 Message-Id: <20230220133602.274842332@linuxfoundation.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230220133600.368809650@linuxfoundation.org> References: <20230220133600.368809650@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Qi Zheng commit badc28d4924bfed73efc93f716a0c3aa3afbdf6f upstream. 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 Signed-off-by: Greg Kroah-Hartman --- 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 +++ b/include/linux/shrinker.h @@ -104,7 +104,7 @@ 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 */ @@ -112,8 +112,9 @@ 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 +++ b/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 +++ b/mm/vmscan.c @@ -740,6 +740,8 @@ EXPORT_SYMBOL(register_shrinker); */ void unregister_shrinker(struct shrinker *shrinker) { + struct dentry *debugfs_entry; + if (!(shrinker->flags & SHRINKER_REGISTERED)) return; @@ -748,9 +750,11 @@ 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; }