Return-Path: Received: from mail-pa0-f42.google.com ([209.85.220.42]:35005 "EHLO mail-pa0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751143AbbIGOFL (ORCPT ); Mon, 7 Sep 2015 10:05:11 -0400 Subject: [PATCH 4/6 v10] fs: New helper legitimize_mntget() for getting a legitimize mnt To: "J. Bruce Fields" , Al Viro References: <55ED9899.9010401@gmail.com> Cc: "linux-nfs@vger.kernel.org" , linux-fsdevel@vger.kernel.org, NeilBrown , Trond Myklebust , kinglongmee@gmail.com From: Kinglong Mee Message-ID: <55ED9986.3040203@gmail.com> Date: Mon, 7 Sep 2015 22:04:54 +0800 MIME-Version: 1.0 In-Reply-To: <55ED9899.9010401@gmail.com> Content-Type: text/plain; charset=utf-8 Sender: linux-nfs-owner@vger.kernel.org List-ID: New helper legitimize_mntget for getting a mnt without setting MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED, otherwise return NULL. v9, Update using read_seqbegin_or_lock instead read_seqlock_excl v10, fix bad logical of using seqlock Signed-off-by: Kinglong Mee --- fs/namespace.c | 38 ++++++++++++++++++++++++++++++++++++++ include/linux/mount.h | 1 + 2 files changed, 39 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index 0570729..6377672 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1153,6 +1153,44 @@ struct vfsmount *mntget(struct vfsmount *mnt) } EXPORT_SYMBOL(mntget); +struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt) +{ + struct mount *mnt; + unsigned seq = 0; + + if (vfsmnt == NULL) + return NULL; + + rcu_read_lock(); +retry: + read_seqbegin_or_lock(&mount_lock, &seq); + + if (vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED)) + vfsmnt = NULL; + else { + mnt = real_mount(vfsmnt); + mnt_add_count(mnt, 1); + if (need_seqretry(&mount_lock, seq)) { + /* lost the race, need to try again */ + if (vfsmnt->mnt_flags & MNT_SYNC_UMOUNT) { + /* no point trying... */ + mnt_add_count(mnt, -1); + vfsmnt = NULL; + } else { + mntput(vfsmnt); + seq = 1; + goto retry; + } + } + } + + done_seqretry(&mount_lock, seq); + rcu_read_unlock(); + + return vfsmnt; +} +EXPORT_SYMBOL(legitimize_mntget); + struct vfsmount *mnt_clone_internal(struct path *path) { struct mount *p; diff --git a/include/linux/mount.h b/include/linux/mount.h index f822c3c..8ae9dc0 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -79,6 +79,7 @@ extern void mnt_drop_write(struct vfsmount *mnt); extern void mnt_drop_write_file(struct file *file); extern void mntput(struct vfsmount *mnt); extern struct vfsmount *mntget(struct vfsmount *mnt); +extern struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt); extern struct vfsmount *mnt_clone_internal(struct path *path); extern int __mnt_is_readonly(struct vfsmount *mnt); -- 2.4.3