From owner-freebsd-fs@freebsd.org Thu Apr 8 22:02:49 2021 Return-Path: Delivered-To: freebsd-fs@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 0D2335C1AF7 for ; Thu, 8 Apr 2021 22:02:49 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4FGZxz5vBRz4lLb for ; Thu, 8 Apr 2021 22:02:47 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.16.1/8.16.1) with ESMTPS id 138M2X7v075732 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Fri, 9 Apr 2021 01:02:36 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua 138M2X7v075732 Received: (from kostik@localhost) by tom.home (8.16.1/8.16.1/Submit) id 138M2X9B075731; Fri, 9 Apr 2021 01:02:33 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Fri, 9 Apr 2021 01:02:33 +0300 From: Konstantin Belousov To: Alexander Lochmann Cc: freebsd-fs Subject: Re: [struct mount] Unprotected access to mnt_secondary_writes Message-ID: References: <5d5cf8de-a262-f6f3-ee0c-6b7ff1a0f095@tu-dortmund.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5d5cf8de-a262-f6f3-ee0c-6b7ff1a0f095@tu-dortmund.de> X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on tom.home X-Rspamd-Queue-Id: 4FGZxz5vBRz4lLb X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=gmail.com (policy=none); spf=softfail (mx1.freebsd.org: 2001:470:d5e7:1::1 is neither permitted nor denied by domain of kostikbel@gmail.com) smtp.mailfrom=kostikbel@gmail.com X-Spamd-Result: default: False [-2.99 / 15.00]; RCVD_TLS_ALL(0.00)[]; ARC_NA(0.00)[]; DMARC_POLICY_SOFTFAIL(0.10)[gmail.com : No valid SPF, No valid DKIM,none]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; FROM_HAS_DN(0.00)[]; RBL_DBL_DONT_QUERY_IPS(0.00)[2001:470:d5e7:1::1:from]; FREEMAIL_FROM(0.00)[gmail.com]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; HAS_XAW(0.00)[]; R_SPF_SOFTFAIL(0.00)[~all]; SPAMHAUS_ZRD(0.00)[2001:470:d5e7:1::1:from:127.0.2.255]; TO_MATCH_ENVRCPT_SOME(0.00)[]; TO_DN_ALL(0.00)[]; NEURAL_HAM_SHORT(-0.99)[-0.986]; RCPT_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:6939, ipnet:2001:470::/32, country:US]; MIME_TRACE(0.00)[0:+]; MAILMAN_DEST(0.00)[freebsd-fs]; RCVD_COUNT_TWO(0.00)[2] X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 08 Apr 2021 22:02:49 -0000 On Thu, Apr 08, 2021 at 05:47:57PM +0200, Alexander Lochmann wrote: > Hi folks! > > According to the documentation [1], and to our findings, mnt_mtx is used to > protect mnt_secondary_writes in struct mount. > However, our data shows that it is accessed in vn_fsync_buf() [2] without > the mnt_mtx lock. I attached the stack trace at the end of this mail. > Our data shows as well that the vnode.v_lock and the vnode.v_bufobj.bo_lock > are being held. > Is this a valid access that ignores the locking on purpose? You mean this line: if ((mp != NULL && mp->mnt_secondary_writes > 0) || It is read access and the possible race is innocent. > Or is it a bug? > > Regards, > Alex > > [1] https://github.com/freebsd/freebsd-src/blob/main/sys/sys/mount.h#L236 > [2] > https://github.com/freebsd/freebsd-src/blob/main/sys/kern/vfs_vnops.c#L2805 > > Stacktrace: > syscall > syscallenter > sys_nmount > vfs_donmount > vfs_domount > vfs_domount_update > ffs_mount > vfs_write_suspend_umnt > vfs_write_suspend > ffs_sync > softdep_flushworklist > VOP_FSYNC > vop_stdfsync > vn_fsync_buf > > -- > Technische Universität Dortmund > Alexander Lochmann PGP key: 0xBC3EF6FD > Otto-Hahn-Str. 16 phone: +49.231.7556141 > D-44227 Dortmund fax: +49.231.7556116 > http://ess.cs.tu-dortmund.de/Staff/al >