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author: Jan Kara <jack@suse.cz> 2023-06-01 12:58:25 +0200 committer: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 2023-07-19 16:36:55 +0200 commit: 059484d31a8a72a2131539713018669350ac34c6 parent: 4cbd5eb173bf0fee1cca3e7dc6d7c2d5fcb93e97
Commit Summary:
fs: Lock moved directories
Diffstat:
2 files changed, 28 insertions, 20 deletions
diff --git a/Documentation/filesystems/directory-locking.rst b/Documentation/filesystems/directory-locking.rst
index 504ba940c36c..dccd61c7c5c3 100644
--- a/Documentation/filesystems/directory-locking.rst
+++ b/Documentation/filesystems/directory-locking.rst
@@ -22,12 +22,11 @@ exclusive.
 3) object removal.  Locking rules: caller locks parent, finds victim,
 locks victim and calls the method.  Locks are exclusive.
 
-4) rename() that is _not_ cross-directory.  Locking rules: caller locks
-the parent and finds source and target.  In case of exchange (with
-RENAME_EXCHANGE in flags argument) lock both.  In any case,
-if the target already exists, lock it.  If the source is a non-directory,
-lock it.  If we need to lock both, lock them in inode pointer order.
-Then call the method.  All locks are exclusive.
+4) rename() that is _not_ cross-directory.  Locking rules: caller locks the
+parent and finds source and target.  We lock both (provided they exist).  If we
+need to lock two inodes of different type (dir vs non-dir), we lock directory
+first.  If we need to lock two inodes of the same type, lock them in inode
+pointer order.  Then call the method.  All locks are exclusive.
 NB: we might get away with locking the source (and target in exchange
 case) shared.
 
@@ -44,15 +43,17 @@ All locks are exclusive.
 rules:
 
 	* lock the filesystem
-	* lock parents in "ancestors first" order.
+	* lock parents in "ancestors first" order. If one is not ancestor of
+	  the other, lock them in inode pointer order.
 	* find source and target.
 	* if old parent is equal to or is a descendent of target
 	  fail with -ENOTEMPTY
 	* if new parent is equal to or is a descendent of source
 	  fail with -ELOOP
-	* If it's an exchange, lock both the source and the target.
-	* If the target exists, lock it.  If the source is a non-directory,
-	  lock it.  If we need to lock both, do so in inode pointer order.
+	* Lock both the source and the target provided they exist. If we
+	  need to lock two inodes of different type (dir vs non-dir), we lock
+	  the directory first. If we need to lock two inodes of the same type,
+	  lock them in inode pointer order.
 	* call the method.
 
 All ->i_rwsem are taken exclusive.  Again, we might get away with locking
@@ -66,8 +67,9 @@ If no directory is its own ancestor, the scheme above is deadlock-free.
 
 Proof:
 
-	First of all, at any moment we have a partial ordering of the
-	objects - A < B iff A is an ancestor of B.
+	First of all, at any moment we have a linear ordering of the
+	objects - A < B iff (A is an ancestor of B) or (B is not an ancestor
+        of A and ptr(A) < ptr(B)).
 
 	That ordering can change.  However, the following is true:
 
diff --git a/fs/namei.c b/fs/namei.c
index 148570aabe74..6a5e26a529e1 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4731,7 +4731,7 @@ SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname
  *	   sb->s_vfs_rename_mutex. We might be more accurate, but that's another
  *	   story.
  *	c) we have to lock _four_ objects - parents and victim (if it exists),
- *	   and source (if it is not a directory).
+ *	   and source.
  *	   And that - after we got ->i_mutex on parents (until then we don't know
  *	   whether the target exists).  Solution: try to be smart with locking
  *	   order for inodes.  We rely on the fact that tree topology may change
@@ -4815,10 +4815,16 @@ int vfs_rename(struct renamedata *rd)
 
 	take_dentry_name_snapshot(&old_name, old_dentry);
 	dget(new_dentry);
-	if (!is_dir || (flags & RENAME_EXCHANGE))
-		lock_two_nondirectories(source, target);
-	else if (target)
-		inode_lock(target);
+	/*
+	 * Lock all moved children. Moved directories may need to change parent
+	 * pointer so they need the lock to prevent against concurrent
+	 * directory changes moving parent pointer. For regular files we've
+	 * historically always done this. The lockdep locking subclasses are
+	 * somewhat arbitrary but RENAME_EXCHANGE in particular can swap
+	 * regular files and directories so it's difficult to tell which
+	 * subclasses to use.
+	 */
+	lock_two_inodes(source, target, I_MUTEX_NORMAL, I_MUTEX_NONDIR2);
 
 	error = -EPERM;
 	if (IS_SWAPFILE(source) || (target && IS_SWAPFILE(target)))
@@ -4866,9 +4872,9 @@ int vfs_rename(struct renamedata *rd)
 			d_exchange(old_dentry, new_dentry);
 	}
 out:
-	if (!is_dir || (flags & RENAME_EXCHANGE))
-		unlock_two_nondirectories(source, target);
-	else if (target)
+	if (source)
+		inode_unlock(source);
+	if (target)
 		inode_unlock(target);
 	dput(new_dentry);
 	if (!error) {