linux-kernel - [PATCH 1/7] vfs - merge path_is_mountpoint() and path_is_mountpoint

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Message-ID: <148029910861.27779.4517883721395202453.stgit@pluto.themaw.net>
Date:   Mon, 28 Nov 2016 10:11:48 +0800
From:   Ian Kent <raven@...maw.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     autofs mailing list <autofs@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Omar Sandoval <osandov@...ndov.com>,
        Al Viro <viro@...IV.linux.org.uk>
Subject: [PATCH 1/7] vfs - merge path_is_mountpoint() and
 path_is_mountpoint_rcu()

From: Ian Kent <ikent@...hat.com>

Forgetting that the rcu lock allows nesting I added a superfluous rcu
version of path_is_mountpoint().

Merge it and the rcu version, make the common case (d_mountpoint()
returning true) inline and change the path parameter to a const.

Also move the function definition to include/linux/mount.h as it
seems a more sensible place for it.

Signed-off-by: Ian Kent <raven@...maw.net>
Cc: Al Viro <viro@...IV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Omar Sandoval <osandov@...ndov.com>
---
 fs/autofs4/root.c     |   11 +++--------
 fs/namespace.c        |   41 ++++++++++++++---------------------------
 include/linux/fs.h    |    2 --
 include/linux/mount.h |   11 +++++++++++
 4 files changed, 28 insertions(+), 37 deletions(-)

diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index c4df881..dd2ea5d 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -437,13 +437,8 @@ static int autofs4_d_manage(struct path *path, bool rcu_walk)
 
 	/* The daemon never waits. */
 	if (autofs4_oz_mode(sbi)) {
-		if (rcu_walk) {
-			if (!path_is_mountpoint_rcu(path))
-				return -EISDIR;
-		} else {
-			if (!path_is_mountpoint(path))
-				return -EISDIR;
-		}
+		if (!path_is_mountpoint(path))
+			return -EISDIR;
 		return 0;
 	}
 
@@ -471,7 +466,7 @@ static int autofs4_d_manage(struct path *path, bool rcu_walk)
 
 		if (ino->flags & AUTOFS_INF_WANT_EXPIRE)
 			return 0;
-		if (path_is_mountpoint_rcu(path))
+		if (path_is_mountpoint(path))
 			return 0;
 		inode = d_inode_rcu(dentry);
 		if (inode && S_ISLNK(inode->i_mode))
diff --git a/fs/namespace.c b/fs/namespace.c
index 79473ee..da1cd87 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1160,12 +1160,23 @@ struct vfsmount *mntget(struct vfsmount *mnt)
 }
 EXPORT_SYMBOL(mntget);
 
-static bool __path_is_mountpoint(struct path *path)
+/* __path_is_mountpoint() - Check if path is a mount in the current
+ *                          namespace.
+ *
+ *  d_mountpoint() can only be used reliably to establish if a dentry is
+ *  not mounted in any namespace and that common case is handled inline.
+ *  d_mountpoint() isn't aware of the possibility there may be multiple
+ *  mounts using a given dentry in a different namespace. This function
+ *  checks if the passed in path is a mountpoint rather than the dentry
+ *  alone.
+ */
+bool __path_is_mountpoint(const struct path *path)
 {
 	struct mount *mount;
 	struct vfsmount *mnt;
 	unsigned seq;
 
+	rcu_read_lock();
 	do {
 		seq = read_seqbegin(&mount_lock);
 		mount = __lookup_mnt(path->mnt, path->dentry);
@@ -1173,35 +1184,11 @@ static bool __path_is_mountpoint(struct path *path)
 	} while (mnt &&
 		 !(mnt->mnt_flags & MNT_SYNC_UMOUNT) &&
 		 read_seqretry(&mount_lock, seq));
-
-	return mnt != NULL;
-}
-
-/* Check if path is a mount in current namespace */
-bool path_is_mountpoint(struct path *path)
-{
-	bool res;
-
-	if (!d_mountpoint(path->dentry))
-		return false;
-
-	rcu_read_lock();
-	res = __path_is_mountpoint(path);
 	rcu_read_unlock();
 
-	return res;
-}
-EXPORT_SYMBOL(path_is_mountpoint);
-
-/* Check if path is a mount in current namespace */
-bool path_is_mountpoint_rcu(struct path *path)
-{
-	if (!d_mountpoint(path->dentry))
-		return false;
-
-	return __path_is_mountpoint(path);
+	return mnt != NULL;
 }
-EXPORT_SYMBOL(path_is_mountpoint_rcu);
+EXPORT_SYMBOL(__path_is_mountpoint);
 
 struct vfsmount *mnt_clone_internal(struct path *path)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 03a5a39..83de8b6 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2095,8 +2095,6 @@ extern int vfs_ustat(dev_t, struct kstatfs *);
 extern int freeze_super(struct super_block *super);
 extern int thaw_super(struct super_block *super);
 extern bool our_mnt(struct vfsmount *mnt);
-extern bool path_is_mountpoint(struct path *);
-extern bool path_is_mountpoint_rcu(struct path *);
 
 extern int current_umask(void);
 
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 1172cce..42dc62b 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -15,6 +15,8 @@
 #include <linux/spinlock.h>
 #include <linux/seqlock.h>
 #include <linux/atomic.h>
+#include <linux/path.h>
+#include <linux/dcache.h>
 
 struct super_block;
 struct vfsmount;
@@ -98,4 +100,13 @@ extern dev_t name_to_dev_t(const char *name);
 
 extern unsigned int sysctl_mount_max;
 
+extern bool __path_is_mountpoint(const struct path *path);
+static inline bool path_is_mountpoint(const struct path *path)
+{
+	if (!d_mountpoint(path->dentry))
+		return 0;
+
+	return __path_is_mountpoint(path);
+}
+
 #endif /* _LINUX_MOUNT_H */