fs: rcu-walk aware d_revalidate method

Require filesystems be aware of .d_revalidate being called in rcu-walk
mode (nd->flags & LOOKUP_RCU). For now do a simple push down, returning
-ECHILD from all implementations.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

1 files changed, 36 insertions, 18 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 90bd2873e117..6e275363e89d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -563,10 +563,26 @@ void release_open_intent(struct nameidata *nd)
                 fput(nd->intent.open.file);
 }
 
+static int d_revalidate(struct dentry *dentry, struct nameidata *nd)
+{
+        int status;
+
+        status = dentry->d_op->d_revalidate(dentry, nd);
+        if (status == -ECHILD) {
+                if (nameidata_dentry_drop_rcu(nd, dentry))
+                        return status;
+                status = dentry->d_op->d_revalidate(dentry, nd);
+        }
+
+        return status;
+}
+
 static inline struct dentry *
 do_revalidate(struct dentry *dentry, struct nameidata *nd)
 {
-        int status = dentry->d_op->d_revalidate(dentry, nd);
+        int status;
+
+        status = d_revalidate(dentry, nd);
         if (unlikely(status <= 0)) {
                 /*
                  * The dentry failed validation.
@@ -574,14 +590,20 @@ do_revalidate(struct dentry *dentry, struct nameidata *nd)
                  * the dentry otherwise d_revalidate is asking us
                  * to return a fail status.
                  */
-                if (!status) {
+                if (status < 0) {
+                        /* If we're in rcu-walk, we don't have a ref */
+                        if (!(nd->flags & LOOKUP_RCU))
+                                dput(dentry);
+                        dentry = ERR_PTR(status);
+
+                } else {
+                        /* Don't d_invalidate in rcu-walk mode */
+                        if (nameidata_dentry_drop_rcu_maybe(nd, dentry))
+                                return ERR_PTR(-ECHILD);
                         if (!d_invalidate(dentry)) {
                                 dput(dentry);
                                 dentry = NULL;
                         }
-                } else {
-                        dput(dentry);
-                        dentry = ERR_PTR(status);
                 }
         }
         return dentry;
@@ -626,7 +648,7 @@ force_reval_path(struct path *path, struct nameidata *nd)
         if (!need_reval_dot(dentry))
                 return 0;
 
-        status = dentry->d_op->d_revalidate(dentry, nd);
+        status = d_revalidate(dentry, nd);
         if (status > 0)
                 return 0;
 
@@ -1039,12 +1061,8 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
                         return -ECHILD;
 
                 nd->seq = seq;
-                if (dentry->d_flags & DCACHE_OP_REVALIDATE) {
-                        /* We commonly drop rcu-walk here */
-                        if (nameidata_dentry_drop_rcu(nd, dentry))
-                                return -ECHILD;
+                if (dentry->d_flags & DCACHE_OP_REVALIDATE)
                         goto need_revalidate;
-                }
                 path->mnt = mnt;
                 path->dentry = dentry;
                 __follow_mount_rcu(nd, path, inode);
@@ -1292,12 +1310,11 @@ return_reval:
                  * We may need to check the cached dentry for staleness.
                  */
                 if (need_reval_dot(nd->path.dentry)) {
-                        if (nameidata_drop_rcu_maybe(nd))
-                                return -ECHILD;
-                        err = -ESTALE;
                         /* Note: we do not d_invalidate() */
-                        if (!nd->path.dentry->d_op->d_revalidate(
-                                        nd->path.dentry, nd))
+                        err = d_revalidate(nd->path.dentry, nd);
+                        if (!err)
+                                err = -ESTALE;
+                        if (err < 0)
                                 break;
                 }
 return_base:
@@ -2080,10 +2097,11 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
                 dir = nd->path.dentry;
         case LAST_DOT:
                 if (need_reval_dot(dir)) {
-                        if (!dir->d_op->d_revalidate(dir, nd)) {
+                        error = d_revalidate(nd->path.dentry, nd);
+                        if (!error)
                                 error = -ESTALE;
+                        if (error < 0)
                                 goto exit;
-                        }
                 }
                 /* fallthrough */
         case LAST_ROOT: