From patchwork Tue Jul 14 16:14:13 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Brauner X-Patchwork-Id: 11663193 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 1926B138C for ; Tue, 14 Jul 2020 16:15:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0AF9422507 for ; Tue, 14 Jul 2020 16:15:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728793AbgGNQPw (ORCPT ); Tue, 14 Jul 2020 12:15:52 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:40914 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726338AbgGNQPt (ORCPT ); Tue, 14 Jul 2020 12:15:49 -0400 Received: from ip5f5af08c.dynamic.kabel-deutschland.de ([95.90.240.140] helo=wittgenstein.fritz.box) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1jvNar-0005y1-4Q; Tue, 14 Jul 2020 16:15:45 +0000 From: Christian Brauner To: David Howells , Al Viro , linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Michael Kerrisk , Christian Brauner Subject: [PATCH 1/4] namespace: take lock_mount_hash() directly when changing flags Date: Tue, 14 Jul 2020 18:14:13 +0200 Message-Id: <20200714161415.3886463-3-christian.brauner@ubuntu.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200714161415.3886463-1-christian.brauner@ubuntu.com> References: <20200714161415.3886463-1-christian.brauner@ubuntu.com> MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Changing mount options always ends up taking lock_mount_hash() but when MNT_READONLY is requested and neither the mount nor the superblock are not already MNT_READONLY we end up taking the lock, dropping it, and retaking it to change the other mount attributes. Instead of this, acquire the lock once when changing mount properties. This simplifies the locking in these codepath, makes them easier to reason about and avoids having to reacquire the lock right after dropping it. Cc: Al Viro Cc: David Howells Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner --- fs/namespace.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index f30ed401cc6d..395b9c912edf 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -463,7 +463,6 @@ static int mnt_make_readonly(struct mount *mnt) { int ret = 0; - lock_mount_hash(); mnt->mnt.mnt_flags |= MNT_WRITE_HOLD; /* * After storing MNT_WRITE_HOLD, we'll read the counters. This store @@ -497,15 +496,12 @@ static int mnt_make_readonly(struct mount *mnt) */ smp_wmb(); mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD; - unlock_mount_hash(); return ret; } static int __mnt_unmake_readonly(struct mount *mnt) { - lock_mount_hash(); mnt->mnt.mnt_flags &= ~MNT_READONLY; - unlock_mount_hash(); return 0; } @@ -2517,11 +2513,9 @@ static int change_mount_ro_state(struct mount *mnt, unsigned int mnt_flags) */ static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags) { - lock_mount_hash(); mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK; mnt->mnt.mnt_flags = mnt_flags; touch_mnt_namespace(mnt->mnt_ns); - unlock_mount_hash(); } static void mnt_warn_timestamp_expiry(struct path *mountpoint, struct vfsmount *mnt) @@ -2567,9 +2561,11 @@ static int do_reconfigure_mnt(struct path *path, unsigned int mnt_flags) return -EPERM; down_write(&sb->s_umount); + lock_mount_hash(); ret = change_mount_ro_state(mnt, mnt_flags); if (ret == 0) set_mount_attributes(mnt, mnt_flags); + unlock_mount_hash(); up_write(&sb->s_umount); mnt_warn_timestamp_expiry(path, &mnt->mnt); @@ -2609,8 +2605,11 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags, err = -EPERM; if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) { err = reconfigure_super(fc); - if (!err) + if (!err) { + lock_mount_hash(); set_mount_attributes(mnt, mnt_flags); + unlock_mount_hash(); + } } up_write(&sb->s_umount); }