[PATCH 04/11] VFS: use d_alloc_parallel() in lookup_one_qstr_excl()

[NeilBrown <neilb@suse.de>]

lookup_one_qstr_excl() is used for lookups prior to directory
modifications, whether create, unlink, rename, or whatever.

To prepare for allowing modification to happen in parallel, change
lookup_one_qstr_excl() to use d_alloc_parallel().

If any for the "intent" LOOKUP flags are passed, the caller must ensure
d_lookup_done() is called at an appropriate time.  If none are passed
then we can be sure ->lookup() will do a real lookup and d_lookup_done()
is called internally.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/namei.c            | 21 ++++++++++++++-------
 fs/smb/server/vfs.c   |  1 +
 include/linux/namei.h |  3 +++
 3 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 174e6693304e..395bfbc8fc92 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1664,11 +1664,9 @@ static struct dentry *lookup_dcache(const struct qstr *name,
 }
 
 /*
- * Parent directory has inode locked exclusive.  This is one
- * and only case when ->lookup() gets called on non in-lookup
- * dentries - as the matter of fact, this only gets called
- * when directory is guaranteed to have no in-lookup children
- * at all.
+ * Parent directory has inode locked exclusive.
+ * If @flags contains any LOOKUP_INTENT_FLAGS then d_lookup_done()
+ * must be called after the intended operation is performed - or aborted.
  */
 struct dentry *lookup_one_qstr_excl(const struct qstr *name,
 				    struct dentry *base,
@@ -1685,15 +1683,22 @@ struct dentry *lookup_one_qstr_excl(const struct qstr *name,
 	if (unlikely(IS_DEADDIR(dir)))
 		return ERR_PTR(-ENOENT);
 
-	dentry = d_alloc(base, name);
-	if (unlikely(!dentry))
+	dentry = d_alloc_parallel(base, name);
+	if (unlikely(IS_ERR_OR_NULL(dentry)))
 		return ERR_PTR(-ENOMEM);
+	if (!d_in_lookup(dentry))
+		/* Raced with another thread which did the lookup */
+		return dentry;
 
 	old = dir->i_op->lookup(dir, dentry, flags);
 	if (unlikely(old)) {
+		d_lookup_done(dentry);
 		dput(dentry);
 		dentry = old;
 	}
+	if ((flags & LOOKUP_INTENT_FLAGS) == 0)
+		/* ->lookup must have given final answer */
+		d_lookup_done(dentry);
 	return dentry;
 }
 EXPORT_SYMBOL(lookup_one_qstr_excl);
@@ -4112,6 +4117,7 @@ static struct dentry *filename_create(int dfd, struct filename *name,
 	}
 	return dentry;
 fail:
+	d_lookup_done(dentry);
 	dput(dentry);
 	dentry = ERR_PTR(error);
 unlock:
@@ -5340,6 +5346,7 @@ int do_renameat2(int olddfd, struct filename *from, int newdfd,
 	rd.flags	   = flags;
 	error = vfs_rename(&rd);
 exit5:
+	d_lookup_done(new_dentry);
 	dput(new_dentry);
 exit4:
 	dput(old_dentry);
diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index dfb0eee5f5f3..83131f08bfb4 100644
--- a/fs/smb/server/vfs.c
+++ b/fs/smb/server/vfs.c
@@ -772,6 +772,7 @@ int ksmbd_vfs_rename(struct ksmbd_work *work, const struct path *old_path,
 		ksmbd_debug(VFS, "vfs_rename failed err %d\n", err);
 
 out4:
+	d_lookup_done(new_dentry);
 	dput(new_dentry);
 out3:
 	dput(old_parent);
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 8ec8fed3bce8..15118992f745 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -34,6 +34,9 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT};
 #define LOOKUP_EXCL		0x0400	/* ... in exclusive creation */
 #define LOOKUP_RENAME_TARGET	0x0800	/* ... in destination of rename() */
 
+#define LOOKUP_INTENT_FLAGS	(LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_EXCL |	\
+				 LOOKUP_RENAME_TARGET)
+
 /* internal use only */
 #define LOOKUP_PARENT		0x0010
 
-- 
2.47.0