From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 05/11] vfs: Add a function to lazily unmount all mounts from any dentry. Date: Sat, 15 Feb 2014 17:50:33 -0800 Message-ID: <87ob27zuza.fsf@xmission.com> References: <87a9kkax0j.fsf@xmission.com> <8761v7h2pt.fsf@tw-ebiederman.twitter.com> <87li281wx6.fsf_-_@xmission.com> <87ob28kqks.fsf_-_@xmission.com> <87txc0jbvt.fsf_-_@xmission.com> Mime-Version: 1.0 Content-Type: text/plain Cc: "Serge E. Hallyn" , Linux-Fsdevel , Kernel Mailing List , Andy Lutomirski , Rob Landley , Linus Torvalds , Miklos Szeredi , Christoph Hellwig , Karel Zak , "J. Bruce Fields" To: Al Viro Return-path: Received: from out02.mta.xmission.com ([166.70.13.232]:40314 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751935AbaBPBvR (ORCPT ); Sat, 15 Feb 2014 20:51:17 -0500 In-Reply-To: <87txc0jbvt.fsf_-_@xmission.com> (Eric W. Biederman's message of "Sat, 15 Feb 2014 13:37:26 -0800") Sender: linux-fsdevel-owner@vger.kernel.org List-ID: ebiederm@xmission.com (Eric W. Biederman) writes: > v2: Always drop the lock when exiting early. > v3: Make detach_mounts robust about freeing several > mounts on the same mountpoint at one time, and remove > the unneeded mnt_list list test. > v4: Document the purpose of detach_mounts and why new_mountpoint is > safe to call. > > Signed-off-by: Eric W. Biederman > --- > fs/mount.h | 2 ++ > fs/namespace.c | 39 +++++++++++++++++++++++++++++++++++++++ > 2 files changed, 41 insertions(+), 0 deletions(-) > > diff --git a/fs/mount.h b/fs/mount.h > index 50a72d46e7a6..2b470f34e665 100644 > --- a/fs/mount.h > +++ b/fs/mount.h > @@ -84,6 +84,8 @@ extern struct mount *__lookup_mnt_last(struct vfsmount *, struct dentry *); > > extern bool legitimize_mnt(struct vfsmount *, unsigned); > > +extern void detach_mounts(struct dentry *dentry); After Linus's rant about performance I took a second look, and lo and behold there is a significant optimization oppportunity missed here. This should almost certainly be: extern void __detach_mounts(struct dentry *dentry); static inline void detach_mounts(struct dentry *dentry) { if (unlikely(d_mountpoint(dentry))) return; __detach_mounts(dentry); } Just so I don't take the namespace lock when not necessary. Although wether this should be inline or at the start of detach_mounts and out of line I don't know. Sigh. I will have to play with this detail a bit more. Eric > static inline void get_mnt_ns(struct mnt_namespace *ns) > { > atomic_inc(&ns->count); > diff --git a/fs/namespace.c b/fs/namespace.c > index 33db9e95bd5c..7abbf722ce18 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -1359,6 +1359,45 @@ static int do_umount(struct mount *mnt, int flags) > return retval; > } > > +/* > + * detach_mounts - lazily unmount all mounts on the specified dentry > + * > + * During unlink, rmdir, and d_drop it is possible to loose the path > + * to an existing mountpoint, and wind up leaking the mount. > + * detach_mounts allows lazily unmounting those mounts instead of > + * leaking them. > + * > + * The caller may hold dentry->d_inode->i_mutex. > + */ > +void detach_mounts(struct dentry *dentry) > +{ > + struct mountpoint *mp; > + struct mount *mnt; > + > + namespace_lock(); > + if (!d_mountpoint(dentry)) > + goto out_unlock; > + > + /* > + * The namespace lock and d_mountpoint being set guarantees > + * that new_mountpoint will just be a lookup of the existing > + * mountpoint structure. > + */ > + mp = new_mountpoint(dentry); > + if (IS_ERR(mp)) > + goto out_unlock; > + > + lock_mount_hash(); > + while (!list_empty(&mp->m_list)) { > + mnt = list_first_entry(&mp->m_list, struct mount, mnt_mp_list); > + umount_tree(mnt, 1); > + } > + unlock_mount_hash(); > + put_mountpoint(mp); > +out_unlock: > + namespace_unlock(); > +} > + > /* > * Is the caller allowed to modify his namespace? > */