From patchwork Wed Oct 19 03:46:40 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Eric W. Biederman" X-Patchwork-Id: 9383565 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 1F2EB600CA for ; Wed, 19 Oct 2016 03:48:58 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id EACC529814 for ; Wed, 19 Oct 2016 03:48:57 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id DC3A92982E; Wed, 19 Oct 2016 03:48:57 +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=-6.9 required=2.0 tests=BAYES_00,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 073F929814 for ; Wed, 19 Oct 2016 03:48:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934582AbcJSDsv (ORCPT ); Tue, 18 Oct 2016 23:48:51 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:55868 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752481AbcJSDsu (ORCPT ); Tue, 18 Oct 2016 23:48:50 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out01.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1bwhs1-0003BN-24; Tue, 18 Oct 2016 21:48:49 -0600 Received: from 75-170-125-99.omah.qwest.net ([75.170.125.99] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1bwhry-0003DR-AU; Tue, 18 Oct 2016 21:48:48 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Andrei Vagin Cc: Andrey Vagin , Alexander Viro , Linux Containers , linux-fsdevel , LKML References: <1476141965-21429-1-git-send-email-avagin@openvz.org> <877f9c6ui8.fsf@x220.int.ebiederm.org> <87pon458l1.fsf_-_@x220.int.ebiederm.org> <20161013214650.GB19836@outlook.office365.com> <87wphb4pjn.fsf@x220.int.ebiederm.org> <8737jy3htt.fsf_-_@x220.int.ebiederm.org> <20161018024000.GA4901@outlook.office365.com> <87r37e9mnj.fsf@xmission.com> Date: Tue, 18 Oct 2016 22:46:40 -0500 In-Reply-To: <87r37e9mnj.fsf@xmission.com> (Eric W. Biederman's message of "Tue, 18 Oct 2016 01:49:52 -0500") Message-ID: <877f95ngpr.fsf_-_@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 X-XM-SPF: eid=1bwhry-0003DR-AU; ; ; mid=<877f95ngpr.fsf_-_@xmission.com>; ; ; hst=in01.mta.xmission.com; ; ; ip=75.170.125.99; ; ; frm=ebiederm@xmission.com; ; ; spf=neutral X-XM-AID: U2FsdGVkX18LUW9Ydh/W8H/2mE0uqbh/BRmelq9KAas= X-SA-Exim-Connect-IP: 75.170.125.99 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: [REVIEW][PATCH] mount: In propagate_umount handle overlapping mount propagation trees X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) 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 Adrei Vagin pointed out that time to executue propagate_umount can go non-linear (and take a ludicrious amount of time) when the mount propogation trees of the mounts to be unmunted by a lazy unmount overlap. While investigating the horrible performance I realized that in the case overlapping mount trees since the addition of locked mount support the code has been failing to unmount all of the mounts it should have been unmounting. Make the walk of the mount propagation trees nearly linear by using MNT_MARK to mark pieces of the mount propagation trees that have already been visited, allowing subsequent walks to skip over subtrees. Make the processing of mounts order independent by adding a list of mount entries that need to be unmounted, and simply adding a mount to that list when it becomes apparent the mount can safely be unmounted. For mounts that are locked on other mounts but otherwise could be unmounted move them from their parnets mnt_mounts to mnt_umounts so that if and when their parent becomes unmounted these mounts can be added to the list of mounts to unmount. Add a final pass to clear MNT_MARK and to restore mnt_mounts from mnt_umounts for anything that did not get unmounted. Add the functions propagation_visit_next and propagation_revisit_next to coordinate walking of the mount tree and setting and clearing the mount mark. The skipping of already unmounted mounts has been moved from __lookup_mnt_last to mark_umount_candidates, so that the new propagation functions can notice when the propagation tree passes through the initial set of unmounted mounts. Except in umount_tree as part of the unmounting process the only place where unmounted mounts should be found are in unmounted subtrees. All of the other callers of __lookup_mnt_last are from mounted subtrees so the not checking for unmounted mounts should not affect them. A script to generate overlapping mount propagation trees: $ cat run.sh mount -t tmpfs test-mount /mnt mount --make-shared /mnt for i in `seq $1`; do mkdir /mnt/test.$i mount --bind /mnt /mnt/test.$i done cat /proc/mounts | grep test-mount | wc -l time umount -l /mnt $ for i in `seq 10 16`; do echo $i; unshare -Urm bash ./run.sh $i; done Here are the performance numbers with and without the patch: mhash | 8192 | 8192 | 8192 | 131072 | 131072 | 104857 | 104857 mounts | before | after | after (sys) | after | after (sys) | after | after (sys) ------------------------------------------------------------------------------------- 1024 | 0.071s | 0.020s | 0.000s | 0.022s | 0.004s | 0.020s | 0.004s 2048 | 0.184s | 0.022s | 0.004s | 0.023s | 0.004s | 0.022s | 0.008s 4096 | 0.604s | 0.025s | 0.020s | 0.029s | 0.008s | 0.026s | 0.004s 8912 | 4.471s | 0.053s | 0.020s | 0.051s | 0.024s | 0.047s | 0.016s 16384 | 34.826s | 0.088s | 0.060s | 0.081s | 0.048s | 0.082s | 0.052s 32768 | | 0.216s | 0.172s | 0.160s | 0.124s | 0.160s | 0.096s 65536 | | 0.819s | 0.726s | 0.330s | 0.260s | 0.338s | 0.256s 131072 | | 4.502s | 4.168s | 0.707s | 0.580s | 0.709s | 0.592s Andrei Vagin reports fixing the performance problem is part of the work to fix CVE-2016-6213. A script for a pathlogical set of mounts: $ cat pathological.sh mount -t tmpfs base /mnt mount --make-shared /mnt mkdir -p /mnt/b mount -t tmpfs test1 /mnt/b mount --make-shared /mnt/b mkdir -p /mnt/b/10 mount -t tmpfs test2 /mnt/b/10 mount --make-shared /mnt/b/10 mkdir -p /mnt/b/10/20 mount --rbind /mnt/b /mnt/b/10/20 unshare -Urm sleep 2 umount -l /mnt/b wait %% $ unsahre -Urm pathlogical.sh Cc: stable@vger.kernel.org Fixes: a05964f3917c ("[PATCH] shared mounts handling: umount") Fixes: 0c56fe31420c ("mnt: Don't propagate unmounts to locked mounts") Reported-by: Andrei Vagin Signed-off-by: "Eric W. Biederman" --- Barring some stupid mistake this looks like it fixes both the performance and the correctness issues I was able to spot earlier. Andrei if you could give this version a look over I would appreciate it. Unless we can find a problem I am going to call this the final version. fs/mount.h | 1 + fs/namespace.c | 7 +- fs/pnode.c | 198 ++++++++++++++++++++++++++++++++++++++++++++++----------- fs/pnode.h | 2 +- 4 files changed, 165 insertions(+), 43 deletions(-) diff --git a/fs/mount.h b/fs/mount.h index d2e25d7b64b3..00fe0d1d6ba7 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -58,6 +58,7 @@ struct mount { struct mnt_namespace *mnt_ns; /* containing namespace */ struct mountpoint *mnt_mp; /* where is it mounted */ struct hlist_node mnt_mp_list; /* list mounts with the same mountpoint */ + struct list_head mnt_umounts; /* list of children that are being unmounted */ #ifdef CONFIG_FSNOTIFY struct hlist_head mnt_fsnotify_marks; __u32 mnt_fsnotify_mask; diff --git a/fs/namespace.c b/fs/namespace.c index e6c234b1a645..73801391bb00 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -237,6 +237,7 @@ static struct mount *alloc_vfsmnt(const char *name) INIT_LIST_HEAD(&mnt->mnt_slave_list); INIT_LIST_HEAD(&mnt->mnt_slave); INIT_HLIST_NODE(&mnt->mnt_mp_list); + INIT_LIST_HEAD(&mnt->mnt_umounts); #ifdef CONFIG_FSNOTIFY INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks); #endif @@ -650,13 +651,11 @@ struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry) p = __lookup_mnt(mnt, dentry); if (!p) goto out; - if (!(p->mnt.mnt_flags & MNT_UMOUNT)) - res = p; + res = p; hlist_for_each_entry_continue(p, mnt_hash) { if (&p->mnt_parent->mnt != mnt || p->mnt_mountpoint != dentry) break; - if (!(p->mnt.mnt_flags & MNT_UMOUNT)) - res = p; + res = p; } out: return res; diff --git a/fs/pnode.c b/fs/pnode.c index 234a9ac49958..15e30e861a14 100644 --- a/fs/pnode.c +++ b/fs/pnode.c @@ -390,56 +390,153 @@ void propagate_mount_unlock(struct mount *mnt) } /* - * Mark all mounts that the MNT_LOCKED logic will allow to be unmounted. + * get the next mount in the propagation tree (that has not been visited) + * @m: the mount seen last + * @origin: the original mount from where the tree walk initiated + * + * Note that peer groups form contiguous segments of slave lists. + * We rely on that in get_source() to be able to find out if + * vfsmount found while iterating with propagation_next() is + * a peer of one we'd found earlier. */ -static void mark_umount_candidates(struct mount *mnt) +static struct mount *propagation_visit_child(struct mount *last_child, + struct mount *origin_child) { - struct mount *parent = mnt->mnt_parent; - struct mount *m; + struct mount *m = last_child->mnt_parent; + struct mount *origin = origin_child->mnt_parent; + struct dentry *mountpoint = origin_child->mnt_mountpoint; + struct mount *child; - BUG_ON(parent == mnt); + /* Has this part of the propgation tree already been visited? */ + if (IS_MNT_MARKED(last_child)) + return NULL; - for (m = propagation_next(parent, parent); m; - m = propagation_next(m, parent)) { - struct mount *child = __lookup_mnt_last(&m->mnt, - mnt->mnt_mountpoint); - if (child && (!IS_MNT_LOCKED(child) || IS_MNT_MARKED(m))) { - SET_MNT_MARK(child); + SET_MNT_MARK(last_child); + + /* are there any slaves of this mount? */ + if (!list_empty(&m->mnt_slave_list)) { + m = first_slave(m); + goto check_slave; + } + while (1) { + struct mount *master = m->mnt_master; + + if (master == origin->mnt_master) { + struct mount *next = next_peer(m); + while (1) { + if (next == origin) + return NULL; + child = __lookup_mnt_last(&next->mnt, mountpoint); + if (child && !IS_MNT_MARKED(child)) + return child; + next = next_peer(next); + } + } else { + while (1) { + if (m->mnt_slave.next == &master->mnt_slave_list) + break; + m = next_slave(m); + check_slave: + child = __lookup_mnt_last(&m->mnt, mountpoint); + if (child && !IS_MNT_MARKED(child)) + return child; + } } + + /* back at master */ + m = master; } } /* - * NOTE: unmounting 'mnt' naturally propagates to all other mounts its - * parent propagates to. + * get the next mount in the propagation tree (that has not been revisited) + * @m: the mount seen last + * @origin: the original mount from where the tree walk initiated + * + * Note that peer groups form contiguous segments of slave lists. + * We rely on that in get_source() to be able to find out if + * vfsmount found while iterating with propagation_next() is + * a peer of one we'd found earlier. */ -static void __propagate_umount(struct mount *mnt) +static struct mount *propagation_revisit_child(struct mount *last_child, + struct mount *origin_child) { - struct mount *parent = mnt->mnt_parent; - struct mount *m; + struct mount *m = last_child->mnt_parent; + struct mount *origin = origin_child->mnt_parent; + struct dentry *mountpoint = origin_child->mnt_mountpoint; + struct mount *child; - BUG_ON(parent == mnt); + /* Has this part of the propgation tree already been revisited? */ + if (!IS_MNT_MARKED(last_child)) + return NULL; - for (m = propagation_next(parent, parent); m; - m = propagation_next(m, parent)) { + CLEAR_MNT_MARK(last_child); - struct mount *child = __lookup_mnt_last(&m->mnt, - mnt->mnt_mountpoint); - /* - * umount the child only if the child has no children - * and the child is marked safe to unmount. - */ - if (!child || !IS_MNT_MARKED(child)) - continue; - CLEAR_MNT_MARK(child); - if (list_empty(&child->mnt_mounts)) { - list_del_init(&child->mnt_child); - child->mnt.mnt_flags |= MNT_UMOUNT; - list_move_tail(&child->mnt_list, &mnt->mnt_list); + /* are there any slaves of this mount? */ + if (!list_empty(&m->mnt_slave_list)) { + m = first_slave(m); + goto check_slave; + } + while (1) { + struct mount *master = m->mnt_master; + + if (master == origin->mnt_master) { + struct mount *next = next_peer(m); + while (1) { + if (next == origin) + return NULL; + child = __lookup_mnt_last(&next->mnt, mountpoint); + if (child && IS_MNT_MARKED(child)) + return child; + next = next_peer(next); + } + } else { + while (1) { + if (m->mnt_slave.next == &master->mnt_slave_list) + break; + m = next_slave(m); + check_slave: + child = __lookup_mnt_last(&m->mnt, mountpoint); + if (child && IS_MNT_MARKED(child)) + return child; + } } + + /* back at master */ + m = master; } } +static void start_umount_propagation(struct mount *child, + struct list_head *to_umount) +{ + do { + struct mount *parent = child->mnt_parent; + + if ((child->mnt.mnt_flags & MNT_UMOUNT) || + !list_empty(&child->mnt_mounts)) + return; + + if (!IS_MNT_LOCKED(child)) + list_move_tail(&child->mnt_child, to_umount); + else + list_move_tail(&child->mnt_child, &parent->mnt_umounts); + + child = NULL; + if (IS_MNT_MARKED(parent)) + child = parent; + } while (child); +} + +static void end_umount_propagation(struct mount *child) +{ + struct mount *parent = child->mnt_parent; + + if (!list_empty(&parent->mnt_umounts)) + list_splice_tail_init(&parent->mnt_umounts, &parent->mnt_mounts); +} + + /* * collect all mounts that receive propagation from the mount in @list, * and return these additional mounts in the same list. @@ -447,14 +544,39 @@ static void __propagate_umount(struct mount *mnt) * * vfsmount lock must be held for write */ -int propagate_umount(struct list_head *list) +void propagate_umount(struct list_head *list) { struct mount *mnt; + LIST_HEAD(to_umount); + LIST_HEAD(tmp_list); + + /* Find candidates for unmounting */ + list_for_each_entry(mnt, list, mnt_list) { + struct mount *child; + for (child = propagation_visit_child(mnt, mnt); child; + child = propagation_visit_child(child, mnt)) + start_umount_propagation(child, &to_umount); + } - list_for_each_entry_reverse(mnt, list, mnt_list) - mark_umount_candidates(mnt); + /* Begin unmounting */ + while (!list_empty(&to_umount)) { + mnt = list_first_entry(&to_umount, struct mount, mnt_child); - list_for_each_entry(mnt, list, mnt_list) - __propagate_umount(mnt); - return 0; + list_del_init(&mnt->mnt_child); + mnt->mnt.mnt_flags |= MNT_UMOUNT; + list_move_tail(&mnt->mnt_list, &tmp_list); + + if (!list_empty(&mnt->mnt_umounts)) + list_splice_tail_init(&mnt->mnt_umounts, &to_umount); + } + + /* Cleanup the mount propagation tree */ + list_for_each_entry(mnt, list, mnt_list) { + struct mount *child; + for (child = propagation_revisit_child(mnt, mnt); child; + child = propagation_revisit_child(child, mnt)) + end_umount_propagation(child); + } + + list_splice_tail(&tmp_list, list); } diff --git a/fs/pnode.h b/fs/pnode.h index 550f5a8b4fcf..38c6cdb96b34 100644 --- a/fs/pnode.h +++ b/fs/pnode.h @@ -41,7 +41,7 @@ static inline void set_mnt_shared(struct mount *mnt) void change_mnt_propagation(struct mount *, int); int propagate_mnt(struct mount *, struct mountpoint *, struct mount *, struct hlist_head *); -int propagate_umount(struct list_head *); +void propagate_umount(struct list_head *); int propagate_mount_busy(struct mount *, int); void propagate_mount_unlock(struct mount *); void mnt_release_group_id(struct mount *);