[PATCH 26/53] smb/client: don't unhashed and rehash to prevent new opens.

[NeilBrown]

From: NeilBrown <neil at brown.name>

smb/client needs to block new opens of the target of unlink and rename
while the operation is progressing.  This stablises d_count() and allows
a determination of whether a "silly-rename" is required.

It currently unhashes the dentry which will cause lookup to block on
the parent directory i_rwsem.  Proposed changes to locking will cause
this approach to stop working and the exclusivity will be provided for
the dentry only, and only while it is hashed.

So we introduce a new machanism similar to that used by nfs and afs.
->d_fsdata (currently unused by smb/client) is set to a non-NULL
value when lookups need to be blocked.  ->d_revalidate checks for this
and blocks.  This might still allow d_count() to increment, but once it
has been tested as 1, there can be no new opens completed.

Signed-off-by: NeilBrown <neil at brown.name>
---
 fs/smb/client/dir.c   |  3 +++
 fs/smb/client/inode.c | 48 +++++++++++++++++--------------------------
 2 files changed, 22 insertions(+), 29 deletions(-)

diff --git a/fs/smb/client/dir.c b/fs/smb/client/dir.c
index cb10088197d2..cecbc0cce5c5 100644
--- a/fs/smb/client/dir.c
+++ b/fs/smb/client/dir.c
@@ -790,6 +790,9 @@ cifs_d_revalidate(struct inode *dir, const struct qstr *name,
 	if (flags & LOOKUP_RCU)
 		return -ECHILD;
 
+	/* Wait for pending rename/unlink */
+	wait_var_event(&direntry->d_fsdata, direntry->d_fsdata == NULL);
+
 	if (d_really_is_positive(direntry)) {
 		int rc;
 		struct inode *inode = d_inode(direntry);
diff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c
index d4d3cfeb6c90..3549605fa9c2 100644
--- a/fs/smb/client/inode.c
+++ b/fs/smb/client/inode.c
@@ -28,6 +28,13 @@
 #include "cached_dir.h"
 #include "reparse.h"
 
+/* This is stored in ->d_fsdata to block d_revalidate on a
+ * file dentry that is being removed - unlink or rename target.
+ * This causes any open attempt to block.  There may be existing opens
+ * but they can be detected by checking d_count() under ->d_lock.
+ */
+#define CIFS_FSDATA_BLOCKED ((void *)1)
+
 /*
  * Set parameters for the netfs library
  */
@@ -1946,27 +1953,21 @@ static int __cifs_unlink(struct inode *dir, struct dentry *dentry, bool sillyren
 	__u32 dosattr = 0, origattr = 0;
 	struct TCP_Server_Info *server;
 	struct iattr *attrs = NULL;
-	bool rehash = false;
 
 	cifs_dbg(FYI, "cifs_unlink, dir=0x%p, dentry=0x%p\n", dir, dentry);
 
 	if (unlikely(cifs_forced_shutdown(cifs_sb)))
 		return smb_EIO(smb_eio_trace_forced_shutdown);
 
-	/* Unhash dentry in advance to prevent any concurrent opens */
-	spin_lock(&dentry->d_lock);
-	if (!d_unhashed(dentry)) {
-		__d_drop(dentry);
-		rehash = true;
-	}
-	spin_unlock(&dentry->d_lock);
-
 	tlink = cifs_sb_tlink(cifs_sb);
 	if (IS_ERR(tlink))
 		return PTR_ERR(tlink);
 	tcon = tlink_tcon(tlink);
 	server = tcon->ses->server;
 
+	/* Set d_fsdata to prevent any concurrent opens */
+	dentry->d_fsdata = CIFS_FSDATA_BLOCKED;
+
 	xid = get_xid();
 	page = alloc_dentry_path();
 
@@ -2083,8 +2084,9 @@ static int __cifs_unlink(struct inode *dir, struct dentry *dentry, bool sillyren
 	kfree(attrs);
 	free_xid(xid);
 	cifs_put_tlink(tlink);
-	if (rehash)
-		d_rehash(dentry);
+
+	/* Allow lookups */
+	store_release_wake_up(&dentry->d_fsdata, NULL);
 	return rc;
 }
 
@@ -2501,7 +2503,6 @@ cifs_rename2(struct mnt_idmap *idmap, struct inode *source_dir,
 	struct cifs_sb_info *cifs_sb;
 	struct tcon_link *tlink;
 	struct cifs_tcon *tcon;
-	bool rehash = false;
 	unsigned int xid;
 	int rc, tmprc;
 	int retry_count = 0;
@@ -2517,23 +2518,15 @@ cifs_rename2(struct mnt_idmap *idmap, struct inode *source_dir,
 	if (unlikely(cifs_forced_shutdown(cifs_sb)))
 		return smb_EIO(smb_eio_trace_forced_shutdown);
 
-	/*
-	 * Prevent any concurrent opens on the target by unhashing the dentry.
-	 * VFS already unhashes the target when renaming directories.
-	 */
-	if (d_is_positive(target_dentry) && !d_is_dir(target_dentry)) {
-		if (!d_unhashed(target_dentry)) {
-			d_drop(target_dentry);
-			rehash = true;
-		}
-	}
-
 	tlink = cifs_sb_tlink(cifs_sb);
 	if (IS_ERR(tlink))
 		return PTR_ERR(tlink);
 	tcon = tlink_tcon(tlink);
 	server = tcon->ses->server;
 
+	/* Set d_fsdata to prevent any concurrent opens */
+	target_dentry->d_fsdata = CIFS_FSDATA_BLOCKED;
+
 	page1 = alloc_dentry_path();
 	page2 = alloc_dentry_path();
 	xid = get_xid();
@@ -2570,8 +2563,6 @@ cifs_rename2(struct mnt_idmap *idmap, struct inode *source_dir,
 		}
 	}
 
-	if (!rc)
-		rehash = false;
 	/*
 	 * No-replace is the natural behavior for CIFS, so skip unlink hacks.
 	 */
@@ -2662,8 +2653,6 @@ cifs_rename2(struct mnt_idmap *idmap, struct inode *source_dir,
 			}
 			rc = cifs_do_rename(xid, source_dentry, from_name,
 					    target_dentry, to_name);
-			if (!rc)
-				rehash = false;
 		}
 	}
 
@@ -2671,8 +2660,9 @@ cifs_rename2(struct mnt_idmap *idmap, struct inode *source_dir,
 	CIFS_I(source_dir)->time = CIFS_I(target_dir)->time = 0;
 
 cifs_rename_exit:
-	if (rehash)
-		d_rehash(target_dentry);
+	/* Allow lookups */
+	store_release_wake_up(&target_dentry->d_fsdata, NULL);
+
 	kfree(info_buf_source);
 	free_dentry_path(page2);
 	free_dentry_path(page1);
-- 
2.50.0.107.gf914562f5916.dirty