[RFC][PATCH v4 12/69] teach handle_mounts() to handle RCU mode

Al Viro
2020-03-13T23:58:12Z

... and make the callers of __follow_mount_rcu() use handle_mounts().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/namei.c | 46 +++++++++++++++++-----------------------------
1 file changed, 17 insertions(+), 29 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 494f4959e790..37b2f82e6f2c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1393,6 +1393,18 @@ static inline int handle_mounts(struct nameidata *nd, struct dentry *dentry,

path->mnt = nd->path.mnt;
path->dentry = dentry;
+ if (nd->flags & LOOKUP_RCU) {
+ unsigned int seq = *seqp;
+ if (unlikely(!*inode))
+ return -ENOENT;
+ if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
+ return 1;
+ if (unlazy_child(nd, dentry, seq))
+ return -ECHILD;
+ // *path might've been clobbered by __follow_mount_rcu()
+ path->mnt = nd->path.mnt;
+ path->dentry = dentry;
+ }
ret = follow_managed(path, nd);
if (likely(ret >= 0)) {
*inode = d_backing_inode(path->dentry);
@@ -1620,7 +1632,6 @@ static int lookup_fast(struct nameidata *nd,
struct path *path, struct inode **inode,
unsigned *seqp)
{
- struct vfsmount *mnt = nd->path.mnt;
struct dentry *dentry, *parent = nd->path.dentry;
int status = 1;

@@ -1658,21 +1669,8 @@ static int lookup_fast(struct nameidata *nd,

*seqp = seq;
status = d_revalidate(dentry, nd->flags);
- if (likely(status > 0)) {
- /*
- * Note: do negative dentry check after revalidation in
- * case that drops it.
- */
- if (unlikely(!inode))
- return -ENOENT;
- path->mnt = mnt;
- path->dentry = dentry;
- if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
- return 1;
- if (unlazy_child(nd, dentry, seq))
- return -ECHILD;
+ if (likely(status > 0))
return handle_mounts(nd, dentry, path, inode, seqp);
- }
if (unlazy_child(nd, dentry, seq))
return -ECHILD;
if (unlikely(status == -ECHILD))
@@ -2361,21 +2359,11 @@ static int handle_lookup_down(struct nameidata *nd)
unsigned seq = nd->seq;
int err;

- if (nd->flags & LOOKUP_RCU) {
- /*
- * don't bother with unlazy_walk on failure - we are
- * at the very beginning of walk, so we lose nothing
- * if we simply redo everything in non-RCU mode
- */
- path = nd->path;
- if (unlikely(!__follow_mount_rcu(nd, &path, &inode, &seq)))
- return -ECHILD;
- } else {
+ if (!(nd->flags & LOOKUP_RCU))
dget(nd->path.dentry);
- err = handle_mounts(nd, nd->path.dentry, &path, &inode, &seq);
- if (unlikely(err < 0))
- return err;
- }
+ err = handle_mounts(nd, nd->path.dentry, &path, &inode, &seq);
+ if (unlikely(err < 0))
+ return err;
path_to_nameidata(&path, nd);
nd->inode = inode;
nd->seq = seq;
--
2.11.0