From patchwork Sat Jul 6 00:22:34 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Al Viro X-Patchwork-Id: 11033497 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 4B9A714F6 for ; Sat, 6 Jul 2019 00:22:59 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 3B1BE28ABC for ; Sat, 6 Jul 2019 00:22:59 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 2F3A728AF8; Sat, 6 Jul 2019 00:22:59 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8D30A28AF2 for ; Sat, 6 Jul 2019 00:22:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727018AbfGFAWo (ORCPT ); Fri, 5 Jul 2019 20:22:44 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:47712 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726038AbfGFAWj (ORCPT ); Fri, 5 Jul 2019 20:22:39 -0400 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92 #3 (Red Hat Linux)) id 1hjYTM-0006o2-LB; Sat, 06 Jul 2019 00:22:36 +0000 From: Al Viro To: linux-fsdevel@vger.kernel.org Cc: Linus Torvalds , linux-kernel@vger.kernel.org Subject: [PATCH 4/6] make struct mountpoint bear the dentry reference to mountpoint, not struct mount Date: Sat, 6 Jul 2019 01:22:34 +0100 Message-Id: <20190706002236.26113-4-viro@ZenIV.linux.org.uk> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190706002236.26113-1-viro@ZenIV.linux.org.uk> References: <20190706001612.GM17978@ZenIV.linux.org.uk> <20190706002236.26113-1-viro@ZenIV.linux.org.uk> MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Al Viro Signed-off-by: Al Viro --- fs/mount.h | 1 - fs/namespace.c | 66 +++++++++++++++++++++++++--------------------------------- 2 files changed, 28 insertions(+), 39 deletions(-) diff --git a/fs/mount.h b/fs/mount.h index 6250de544760..84aa8cdf4971 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -69,7 +69,6 @@ struct mount { int mnt_expiry_mark; /* true if marked for expiry */ struct hlist_head mnt_pins; struct fs_pin mnt_umount; - struct dentry *mnt_ex_mountpoint; } __randomize_layout; #define MNT_NS_INTERNAL ERR_PTR(-EINVAL) /* distinct from any mnt_namespace */ diff --git a/fs/namespace.c b/fs/namespace.c index b7059a4f07e3..911675de2a70 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -69,6 +69,8 @@ static struct hlist_head *mount_hashtable __read_mostly; static struct hlist_head *mountpoint_hashtable __read_mostly; static struct kmem_cache *mnt_cache __read_mostly; static DECLARE_RWSEM(namespace_sem); +static HLIST_HEAD(unmounted); /* protected by namespace_sem */ +static LIST_HEAD(ex_mountpoints); /* /sys/fs */ struct kobject *fs_kobj; @@ -172,7 +174,6 @@ unsigned int mnt_get_count(struct mount *mnt) static void drop_mountpoint(struct fs_pin *p) { struct mount *m = container_of(p, struct mount, mnt_umount); - dput(m->mnt_ex_mountpoint); pin_remove(p); mntput(&m->mnt); } @@ -739,7 +740,7 @@ static struct mountpoint *get_mountpoint(struct dentry *dentry) /* Add the new mountpoint to the hash table */ read_seqlock_excl(&mount_lock); - new->m_dentry = dentry; + new->m_dentry = dget(dentry); new->m_count = 1; hlist_add_head(&new->m_hash, mp_hash(dentry)); INIT_HLIST_HEAD(&new->m_list); @@ -752,7 +753,7 @@ static struct mountpoint *get_mountpoint(struct dentry *dentry) return mp; } -static void put_mountpoint(struct mountpoint *mp) +static void put_mountpoint(struct mountpoint *mp, struct list_head *list) { if (!--mp->m_count) { struct dentry *dentry = mp->m_dentry; @@ -760,6 +761,9 @@ static void put_mountpoint(struct mountpoint *mp) spin_lock(&dentry->d_lock); dentry->d_flags &= ~DCACHE_MOUNTED; spin_unlock(&dentry->d_lock); + if (!list) + list = &ex_mountpoints; + dput_to_list(dentry, list); hlist_del(&mp->m_hash); kfree(mp); } @@ -813,19 +817,17 @@ static struct mountpoint *unhash_mnt(struct mount *mnt) */ static void detach_mnt(struct mount *mnt, struct path *old_path) { - old_path->dentry = mnt->mnt_mountpoint; + old_path->dentry = dget(mnt->mnt_mountpoint); old_path->mnt = &mnt->mnt_parent->mnt; - put_mountpoint(unhash_mnt(mnt)); + put_mountpoint(unhash_mnt(mnt), NULL); } /* * vfsmount lock must be held for write */ -static void umount_mnt(struct mount *mnt) +static void umount_mnt(struct mount *mnt, struct list_head *list) { - /* old mountpoint will be dropped when we can do that */ - mnt->mnt_ex_mountpoint = mnt->mnt_mountpoint; - put_mountpoint(unhash_mnt(mnt)); + put_mountpoint(unhash_mnt(mnt), list); } /* @@ -837,7 +839,7 @@ void mnt_set_mountpoint(struct mount *mnt, { mp->m_count++; mnt_add_count(mnt, 1); /* essentially, that's mntget */ - child_mnt->mnt_mountpoint = dget(mp->m_dentry); + child_mnt->mnt_mountpoint = mp->m_dentry; child_mnt->mnt_parent = mnt; child_mnt->mnt_mp = mp; hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list); @@ -864,7 +866,6 @@ static void attach_mnt(struct mount *mnt, void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct mount *mnt) { struct mountpoint *old_mp = mnt->mnt_mp; - struct dentry *old_mountpoint = mnt->mnt_mountpoint; struct mount *old_parent = mnt->mnt_parent; list_del_init(&mnt->mnt_child); @@ -873,23 +874,7 @@ void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct m attach_mnt(mnt, parent, mp); - put_mountpoint(old_mp); - - /* - * Safely avoid even the suggestion this code might sleep or - * lock the mount hash by taking advantage of the knowledge that - * mnt_change_mountpoint will not release the final reference - * to a mountpoint. - * - * During mounting, the mount passed in as the parent mount will - * continue to use the old mountpoint and during unmounting, the - * old mountpoint will continue to exist until namespace_unlock, - * which happens well after mnt_change_mountpoint. - */ - spin_lock(&old_mountpoint->d_lock); - old_mountpoint->d_lockref.count--; - spin_unlock(&old_mountpoint->d_lock); - + put_mountpoint(old_mp, NULL); mnt_add_count(old_parent, -1); } @@ -1142,6 +1127,8 @@ static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput); static void mntput_no_expire(struct mount *mnt) { + LIST_HEAD(list); + rcu_read_lock(); if (likely(READ_ONCE(mnt->mnt_ns))) { /* @@ -1182,10 +1169,11 @@ static void mntput_no_expire(struct mount *mnt) if (unlikely(!list_empty(&mnt->mnt_mounts))) { struct mount *p, *tmp; list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts, mnt_child) { - umount_mnt(p); + umount_mnt(p, &list); } } unlock_mount_hash(); + shrink_dentry_list(&list); if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) { struct task_struct *task = current; @@ -1371,16 +1359,18 @@ int may_umount(struct vfsmount *mnt) EXPORT_SYMBOL(may_umount); -static HLIST_HEAD(unmounted); /* protected by namespace_sem */ - static void namespace_unlock(void) { struct hlist_head head; + LIST_HEAD(list); hlist_move_list(&unmounted, &head); + list_splice_init(&ex_mountpoints, &list); up_write(&namespace_sem); + shrink_dentry_list(&list); + if (likely(hlist_empty(&head))) return; @@ -1481,7 +1471,7 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how) /* Don't forget about p */ list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts); } else { - umount_mnt(p); + umount_mnt(p, NULL); } } change_mnt_propagation(p, MS_PRIVATE); @@ -1635,11 +1625,11 @@ void __detach_mounts(struct dentry *dentry) mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list); if (mnt->mnt.mnt_flags & MNT_UMOUNT) { hlist_add_head(&mnt->mnt_umount.s_list, &unmounted); - umount_mnt(mnt); + umount_mnt(mnt, NULL); } else umount_tree(mnt, UMOUNT_CONNECTED); } - put_mountpoint(mp); + put_mountpoint(mp, NULL); out_unlock: unlock_mount_hash(); namespace_unlock(); @@ -2110,7 +2100,7 @@ static int attach_recursive_mnt(struct mount *source_mnt, child->mnt.mnt_flags &= ~MNT_LOCKED; commit_tree(child); } - put_mountpoint(smp); + put_mountpoint(smp, NULL); unlock_mount_hash(); return 0; @@ -2127,7 +2117,7 @@ static int attach_recursive_mnt(struct mount *source_mnt, ns->pending_mounts = 0; read_seqlock_excl(&mount_lock); - put_mountpoint(smp); + put_mountpoint(smp, NULL); read_sequnlock_excl(&mount_lock); return err; @@ -2167,7 +2157,7 @@ static void unlock_mount(struct mountpoint *where) struct dentry *dentry = where->m_dentry; read_seqlock_excl(&mount_lock); - put_mountpoint(where); + put_mountpoint(where, NULL); read_sequnlock_excl(&mount_lock); namespace_unlock(); @@ -3663,7 +3653,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root, touch_mnt_namespace(current->nsproxy->mnt_ns); /* A moved mount should not expire automatically */ list_del_init(&new_mnt->mnt_expire); - put_mountpoint(root_mp); + put_mountpoint(root_mp, NULL); unlock_mount_hash(); chroot_fs_refs(&root, &new); error = 0;