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 76670C433FE for ; Tue, 8 Nov 2022 23:58:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230078AbiKHX6X (ORCPT ); Tue, 8 Nov 2022 18:58:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51228 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229868AbiKHX6N (ORCPT ); Tue, 8 Nov 2022 18:58:13 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9654B6068C; Tue, 8 Nov 2022 15:58:12 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 3334E617E2; Tue, 8 Nov 2022 23:58:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8A56DC433D6; Tue, 8 Nov 2022 23:58:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1667951891; bh=kBieeZP7ebC1ESMLsmykoSU2QtaDOK8PQV+EQT7FxQo=; h=Date:To:From:Subject:From; b=F0GorJE7er1aLb/WCvIbw4Gz/YP+85sH0Huqm6qJtzr4Oo52G2WuHDHT2ayu1KE3t ocoWMWZNLv6KO7yfkmLGhD2uE/2X9PyFRfGdMBPGWF7brh8tB7UDNVjaJtLsSc4086 u7SXnawRdMamoCf5skKrC2c9Qn84qsB96H9gbjJw= Date: Tue, 08 Nov 2022 15:58:11 -0800 To: mm-commits@vger.kernel.org, stable@vger.kernel.org, konishi.ryusuke@gmail.com, akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] nilfs2-fix-deadlock-in-nilfs_count_free_blocks.patch removed from -mm tree Message-Id: <20221108235811.8A56DC433D6@smtp.kernel.org> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The quilt patch titled Subject: nilfs2: fix deadlock in nilfs_count_free_blocks() has been removed from the -mm tree. Its filename was nilfs2-fix-deadlock-in-nilfs_count_free_blocks.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: Ryusuke Konishi Subject: nilfs2: fix deadlock in nilfs_count_free_blocks() Date: Sat, 29 Oct 2022 13:49:12 +0900 A semaphore deadlock can occur if nilfs_get_block() detects metadata corruption while locating data blocks and a superblock writeback occurs at the same time: task 1 task 2 ------ ------ * A file operation * nilfs_truncate() nilfs_get_block() down_read(rwsem A) <-- nilfs_bmap_lookup_contig() ... generic_shutdown_super() nilfs_put_super() * Prepare to write superblock * down_write(rwsem B) <-- nilfs_cleanup_super() * Detect b-tree corruption * nilfs_set_log_cursor() nilfs_bmap_convert_error() nilfs_count_free_blocks() __nilfs_error() down_read(rwsem A) <-- nilfs_set_error() down_write(rwsem B) <-- *** DEADLOCK *** Here, nilfs_get_block() readlocks rwsem A (= NILFS_MDT(dat_inode)->mi_sem) and then calls nilfs_bmap_lookup_contig(), but if it fails due to metadata corruption, __nilfs_error() is called from nilfs_bmap_convert_error() inside the lock section. Since __nilfs_error() calls nilfs_set_error() unless the filesystem is read-only and nilfs_set_error() attempts to writelock rwsem B (= nilfs->ns_sem) to write back superblock exclusively, hierarchical lock acquisition occurs in the order rwsem A -> rwsem B. Now, if another task starts updating the superblock, it may writelock rwsem B during the lock sequence above, and can deadlock trying to readlock rwsem A in nilfs_count_free_blocks(). However, there is actually no need to take rwsem A in nilfs_count_free_blocks() because it, within the lock section, only reads a single integer data on a shared struct with nilfs_sufile_get_ncleansegs(). This has been the case after commit aa474a220180 ("nilfs2: add local variable to cache the number of clean segments"), that is, even before this bug was introduced. So, this resolves the deadlock problem by just not taking the semaphore in nilfs_count_free_blocks(). Link: https://lkml.kernel.org/r/20221029044912.9139-1-konishi.ryusuke@gmail.com Fixes: e828949e5b42 ("nilfs2: call nilfs_error inside bmap routines") Signed-off-by: Ryusuke Konishi Reported-by: syzbot+45d6ce7b7ad7ef455d03@syzkaller.appspotmail.com Tested-by: Ryusuke Konishi Cc: [2.6.38+ Signed-off-by: Andrew Morton --- fs/nilfs2/the_nilfs.c | 2 -- 1 file changed, 2 deletions(-) --- a/fs/nilfs2/the_nilfs.c~nilfs2-fix-deadlock-in-nilfs_count_free_blocks +++ a/fs/nilfs2/the_nilfs.c @@ -690,9 +690,7 @@ int nilfs_count_free_blocks(struct the_n { unsigned long ncleansegs; - down_read(&NILFS_MDT(nilfs->ns_dat)->mi_sem); ncleansegs = nilfs_sufile_get_ncleansegs(nilfs->ns_sufile); - up_read(&NILFS_MDT(nilfs->ns_dat)->mi_sem); *nblocks = (sector_t)ncleansegs * nilfs->ns_blocks_per_segment; return 0; } _ Patches currently in -mm which might be from konishi.ryusuke@gmail.com are nilfs2-fix-shift-out-of-bounds-overflow-in-nilfs_sb2_bad_offset.patch nilfs2-fix-shift-out-of-bounds-due-to-too-large-exponent-of-block-size.patch