[RFC][PATCH v3 29/55] massage __follow_mount_rcu() a bit

Al Viro
2020-03-01T21:54:18Z

make the loop more similar to that in follow_managed(), with
explicit tracking of flags, etc.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 70 +++++++++++++++++++++++++++++++-------------------------------
1 file changed, 35 insertions(+), 35 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 5fe499399fcb..02cdd1208062 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1269,12 +1269,6 @@ int follow_down_one(struct path *path)
}
EXPORT_SYMBOL(follow_down_one);

-static inline int managed_dentry_rcu(const struct path *path)
-{
- return (path->dentry->d_flags & DCACHE_MANAGE_TRANSIT) ?
- path->dentry->d_op->d_manage(path, true) : 0;
-}
-
/*
* Try to skip to top of mountpoint pile in rcuwalk mode. Fail if
* we meet a managed dentry that would need blocking.
@@ -1282,43 +1276,49 @@ static inline int managed_dentry_rcu(const struct path *path)
static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
struct inode **inode, unsigned *seqp)
{
+ struct dentry *dentry = path->dentry;
+ unsigned int flags = dentry->d_flags;
+
+ if (likely(!(flags & DCACHE_MANAGED_DENTRY)))
+ return true;
+
+ if (unlikely(nd->flags & LOOKUP_NO_XDEV))
+ return false;
+
for (;;) {
- struct mount *mounted;
/*
* Don't forget we might have a non-mountpoint managed dentry
* that wants to block transit.
*/
- switch (managed_dentry_rcu(path)) {
- case -ECHILD:
- default:
- return false;
- case -EISDIR:
- return true;
- case 0:
- break;
+ if (unlikely(flags & DCACHE_MANAGE_TRANSIT)) {
+ int res = dentry->d_op->d_manage(path, true);
+ if (res)
+ return res == -EISDIR;
+ flags = dentry->d_flags;
}

- if (!d_mountpoint(path->dentry))
- return !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
-
- mounted = __lookup_mnt(path->mnt, path->dentry);
- if (!mounted)
- break;
- if (unlikely(nd->flags & LOOKUP_NO_XDEV))
- return false;
- path->mnt = &mounted->mnt;
- path->dentry = mounted->mnt.mnt_root;
- nd->flags |= LOOKUP_JUMPED;
- *seqp = read_seqcount_begin(&path->dentry->d_seq);
- /*
- * Update the inode too. We don't need to re-check the
- * dentry sequence number here after this d_inode read,
- * because a mount-point is always pinned.
- */
- *inode = path->dentry->d_inode;
+ if (flags & DCACHE_MOUNTED) {
+ struct mount *mounted = __lookup_mnt(path->mnt, dentry);
+ if (mounted) {
+ path->mnt = &mounted->mnt;
+ dentry = path->dentry = mounted->mnt.mnt_root;
+ nd->flags |= LOOKUP_JUMPED;
+ *seqp = read_seqcount_begin(&dentry->d_seq);
+ *inode = dentry->d_inode;
+ /*
+ * We don't need to re-check ->d_seq after this
+ * ->d_inode read - there will be an RCU delay
+ * between mount hash removal and ->mnt_root
+ * becoming unpinned.
+ */
+ flags = dentry->d_flags;
+ continue;
+ }
+ if (read_seqretry(&mount_lock, nd->m_seq))
+ return false;
+ }
+ return !(flags & DCACHE_NEED_AUTOMOUNT);
}
- return !read_seqretry(&mount_lock, nd->m_seq) &&
- !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
}

static inline int handle_mounts(struct nameidata *nd, struct dentry *dentry,
--
2.11.0