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[89.243.172.161]) by smtp.gmail.com with ESMTPSA id x15-v6sm14550241wrt.90.2018.10.19.10.35.51 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Oct 2018 10:35:51 -0700 (PDT) Subject: Re: [PATCH 03/34] teach move_mount(2) to work with OPEN_TREE_CLONE [ver #12] To: David Howells , viro@zeniv.linux.org.uk Cc: torvalds@linux-foundation.org, ebiederm@xmission.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, mszeredi@redhat.com References: <862e36a2-2a6f-4e26-3228-8cab4b4cf230@gmail.com> <153754740781.17872.7869536526927736855.stgit@warthog.procyon.org.uk> <153754743491.17872.12115848333103740766.stgit@warthog.procyon.org.uk> <6518.1539956277@warthog.procyon.org.uk> From: Alan Jenkins Message-ID: <97872123-70be-2833-ea7a-a463ce204b53@gmail.com> Date: Fri, 19 Oct 2018 18:35:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <6518.1539956277@warthog.procyon.org.uk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/10/2018 14:37, David Howells wrote: > Alan Jenkins wrote: > >> If I close() the mount FD "mfd", and then do "mount --move . /mnt", my >> printk() shows MNT_UMOUNT has been set. ( I guess fchdir() works more like >> openat(... , O_PATH) than dup() ). Then unmounting /mnt hangs, as I would >> expect from my previous test. > Okay, I think the attached should fix it. > > The issue being that do_move_mount() calls attach_recursive_mnt() with a NULL > parent_path, which means that the moved-mount doesn't get its refcount > incremented. > > David > --- > diff --git a/fs/namespace.c b/fs/namespace.c > index 6370bfabec99..ce9fff980549 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -1935,7 +1935,8 @@ int count_mounts(struct mnt_namespace *ns, struct mount *mnt) > static int attach_recursive_mnt(struct mount *source_mnt, > struct mount *dest_mnt, > struct mountpoint *dest_mp, > - struct path *parent_path) > + struct path *parent_path, > + bool moving) > { > HLIST_HEAD(tree_list); > struct mnt_namespace *ns = dest_mnt->mnt_ns; > @@ -1976,6 +1977,8 @@ static int attach_recursive_mnt(struct mount *source_mnt, > attach_mnt(source_mnt, dest_mnt, dest_mp); > touch_mnt_namespace(source_mnt->mnt_ns); > } else { > + if (moving) > + mnt_add_count(source_mnt, 1); > mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt); > commit_tree(source_mnt); > } > @@ -2062,7 +2065,7 @@ static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp) > d_is_dir(mnt->mnt.mnt_root)) > return -ENOTDIR; > > - return attach_recursive_mnt(mnt, p, mp, NULL); > + return attach_recursive_mnt(mnt, p, mp, NULL, false); > } > > /* > @@ -2522,7 +2525,7 @@ static int do_move_mount(struct path *old_path, struct path *new_path) > goto out1; > > err = attach_recursive_mnt(old, real_mount(new_path->mnt), mp, > - attached ? &parent_path : NULL); > + attached ? &parent_path : NULL, true); > if (err) > goto out1; > I guess this tries to fix the second of the two sequences I mentioned - mount+unmount, then close the FD.  It doesn't seem to work. # open_tree_clone 3mnt_ns && !attached) goto out1; - if (old->mnt.mnt_flags & MNT_LOCKED) + if (old->mnt.mnt_flags & (MNT_LOCKED | MNT_UMOUNT)) goto out1; if (old_path->dentry != old_path->mnt->mnt_root) If we can do that, then is it possible to solve mount-unmount-close the same way? @@ -1763,7 +1763,7 @@ void dissolve_on_fput(struct vfsmount *mnt) { namespace_lock(); lock_mount_hash(); - if (!real_mount(mnt)->mnt_ns) { + if (!real_mount(mnt)->mnt_ns && !(mnt->mnt_flags & MNT_UMOUNT)) { mntget(mnt); umount_tree(real_mount(mnt), UMOUNT_CONNECTED); } Regards Alan