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From 0c0bf47e3e77ebff691abe1a5e133e43515e5205 Mon Sep 17 00:00:00 2001
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From: "T.kabe" <kabe@>
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Date: Mon, 6 Mar 2017 15:21:16 +0900
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Subject: [PATCH 3/4] vfs: Add a function to lazily unmount all mounts from any dentry.
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[upstream commit 80b5dce8c59b0de1ed6e403b8298e02dcb4db64b]
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Author: Eric W. Biederman <ebiederman@twitter.com>
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Date:   Thu Oct 3 01:31:18 2013 -0700
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    vfs: Add a function to lazily unmount all mounts from any dentry.
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    The new function detach_mounts comes in two pieces.  The first piece
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    is a static inline test of d_mounpoint that returns immediately
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    without taking any locks if d_mounpoint is not set.  In the common
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    case when mountpoints are absent this allows the vfs to continue
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    running with it's same cacheline foot print.
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    The second piece of detach_mounts __detach_mounts actually does the
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    work and it assumes that a mountpoint is present so it is slow and
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    takes namespace_sem for write, and then locks the mount hash (aka
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    mount_lock) after a struct mountpoint has been found.
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    With those two locks held each entry on the list of mounts on a
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    mountpoint is selected and lazily unmounted until all of the mount
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    have been lazily unmounted.
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    v7: Wrote a proper change description and removed the changelog
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        documenting deleted wrong turns.
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    Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>
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    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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---
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 fs/mount.h     |  9 +++++++++
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 fs/namespace.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
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 2 files changed, 57 insertions(+)
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diff --git a/fs/mount.h b/fs/mount.h
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index 92fecbe..9959119 100644
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--- a/fs/mount.h
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+++ b/fs/mount.h
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@@ -80,6 +80,15 @@ static inline int is_mounted(struct vfsmount *mnt)
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 extern struct mount *__lookup_mnt(struct vfsmount *, struct dentry *, int);
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+extern void __detach_mounts(struct dentry *dentry);
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+
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+static inline void detach_mounts(struct dentry *dentry)
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+{
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+	if (!d_mountpoint(dentry))
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+		return;
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+	__detach_mounts(dentry);
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+}
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+
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 static inline void get_mnt_ns(struct mnt_namespace *ns)
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 {
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 	atomic_inc(&ns->count);
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diff --git a/fs/namespace.c b/fs/namespace.c
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index c238481..e48fed3 100644
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--- a/fs/namespace.c
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+++ b/fs/namespace.c
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@@ -608,6 +608,23 @@ struct vfsmount *lookup_mnt(struct path *path)
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 	}
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 }
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+static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
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+{
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+	struct list_head *chain = mountpoint_hashtable + hash(NULL, dentry);
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+	struct mountpoint *mp;
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+
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+	list_for_each_entry(mp, chain, m_hash) {
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+		if (mp->m_dentry == dentry) {
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+			/* might be worth a WARN_ON() */
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+			if (d_unlinked(dentry))
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+				return ERR_PTR(-ENOENT);
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+			mp->m_count++;
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+			return mp;
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+		}
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+	}
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+	return NULL;
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+}
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+
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 static struct mountpoint *new_mountpoint(struct dentry *dentry)
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 {
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 	struct list_head *chain = mountpoint_hashtable + hash(NULL, dentry);
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@@ -1312,6 +1329,37 @@ static int do_umount(struct mount *mnt, int flags)
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 	return retval;
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 }
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+/*
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+ * __detach_mounts - lazily unmount all mounts on the specified dentry
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+ *
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+ * During unlink, rmdir, and d_drop it is possible to loose the path
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+ * to an existing mountpoint, and wind up leaking the mount.
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+ * detach_mounts allows lazily unmounting those mounts instead of
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+ * leaking them.
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+ *
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+ * The caller may hold dentry->d_inode->i_mutex.
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+ */
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+void __detach_mounts(struct dentry *dentry)
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+{
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+	struct mountpoint *mp;
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+	struct mount *mnt;
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+
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+	namespace_lock();
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+	mp = lookup_mountpoint(dentry);
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+	if (!mp)
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+		goto out_unlock;
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+
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+	br_write_lock(&vfsmount_lock);
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+	while (!hlist_empty(&mp->m_list)) {
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+		mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
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+		umount_tree(mnt, 2);
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+	}
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+	br_write_unlock(&vfsmount_lock);
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+	put_mountpoint(mp);
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+out_unlock:
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+	namespace_unlock();
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+}
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+
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 /* 
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  * Is the caller allowed to modify his namespace?
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  */
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-- 
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1.8.3.1
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