Merge branch 'stable-fodder' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull vfs stable fodder fixes from Al Viro:

 - acct_on() fix for deadlock caught by overlayfs folks

 - autofs RCU use-after-free SNAFU (->d_manage() can be called
   locklessly, so we need to RCU-delay freeing the objects it looks at)

 - (hopefully) the end of "do we need freeing this dentry RCU-delayed"
   whack-a-mole.

* 'stable-fodder' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  autofs: fix use-after-free in lockless ->d_manage()
  dcache: sort the freeing-without-RCU-delay mess for good.
  acct_on(): don't mess with freeze protection

Documentation/filesystems/porting

@@ -663,3 +663,8 @@ in your dentry operations instead.
 	there, but that's it.  Freeing memory in the callback is fine; doing
 	more than that is possible, but requires a lot of care and is best
 	avoided.
+--
+[mandatory]
+	DCACHE_RCUACCESS is gone; having an RCU delay on dentry freeing is the
+	default.  DCACHE_NORCU opts out, and only d_alloc_pseudo() has any
+	business doing so.

fs/autofs/autofs_i.h

@@ -71,6 +71,7 @@ struct autofs_info {
 
 	kuid_t uid;
 	kgid_t gid;
+	struct rcu_head rcu;
 };
 
 #define AUTOFS_INF_EXPIRING	(1<<0) /* dentry in the process of expiring */

fs/autofs/inode.c

@@ -36,7 +36,7 @@ void autofs_clean_ino(struct autofs_info *ino)
 
 void autofs_free_ino(struct autofs_info *ino)
 {
-	kfree(ino);
+	kfree_rcu(ino, rcu);
 }
 
 void autofs_kill_sb(struct super_block *sb)

fs/dcache.c

@@ -344,7 +344,7 @@ static void dentry_free(struct dentry *dentry)
 		}
 	}
 	/* if dentry was never visible to RCU, immediate free is OK */
-	if (!(dentry->d_flags & DCACHE_RCUACCESS))
+	if (dentry->d_flags & DCACHE_NORCU)
 		__d_free(&dentry->d_u.d_rcu);
 	else
 		call_rcu(&dentry->d_u.d_rcu, __d_free);
@@ -1701,7 +1701,6 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
 	struct dentry *dentry = __d_alloc(parent->d_sb, name);
 	if (!dentry)
 		return NULL;
-	dentry->d_flags |= DCACHE_RCUACCESS;
 	spin_lock(&parent->d_lock);
 	/*
 	 * don't need child lock because it is not subject
@@ -1726,7 +1725,7 @@ struct dentry *d_alloc_cursor(struct dentry * parent)
 {
 	struct dentry *dentry = d_alloc_anon(parent->d_sb);
 	if (dentry) {
-		dentry->d_flags |= DCACHE_RCUACCESS | DCACHE_DENTRY_CURSOR;
+		dentry->d_flags |= DCACHE_DENTRY_CURSOR;
 		dentry->d_parent = dget(parent);
 	}
 	return dentry;
@@ -1739,10 +1738,17 @@ struct dentry *d_alloc_cursor(struct dentry * parent)
  *
  * For a filesystem that just pins its dentries in memory and never
  * performs lookups at all, return an unhashed IS_ROOT dentry.
+ * This is used for pipes, sockets et.al. - the stuff that should
+ * never be anyone's children or parents.  Unlike all other
+ * dentries, these will not have RCU delay between dropping the
+ * last reference and freeing them.
  */
 struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
 {
-	return __d_alloc(sb, name);
+	struct dentry *dentry = __d_alloc(sb, name);
+	if (likely(dentry))
+		dentry->d_flags |= DCACHE_NORCU;
+	return dentry;
 }
 EXPORT_SYMBOL(d_alloc_pseudo);
 
@@ -1911,12 +1917,10 @@ struct dentry *d_make_root(struct inode *root_inode)
 
 	if (root_inode) {
 		res = d_alloc_anon(root_inode->i_sb);
-		if (res) {
-			res->d_flags |= DCACHE_RCUACCESS;
+		if (res)
 			d_instantiate(res, root_inode);
-		} else {
+		else
 			iput(root_inode);
-		}
 	}
 	return res;
 }
@@ -2781,9 +2785,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
 		copy_name(dentry, target);
 		target->d_hash.pprev = NULL;
 		dentry->d_parent->d_lockref.count++;
-		if (dentry == old_parent)
-			dentry->d_flags |= DCACHE_RCUACCESS;
-		else
+		if (dentry != old_parent) /* wasn't IS_ROOT */
 			WARN_ON(!--old_parent->d_lockref.count);
 	} else {
 		target->d_parent = old_parent;

fs/internal.h

@@ -89,9 +89,7 @@ extern int sb_prepare_remount_readonly(struct super_block *);
 
 extern void __init mnt_init(void);
 
-extern int __mnt_want_write(struct vfsmount *);
 extern int __mnt_want_write_file(struct file *);
-extern void __mnt_drop_write(struct vfsmount *);
 extern void __mnt_drop_write_file(struct file *);
 
 /*

fs/nsfs.c

@@ -85,13 +85,12 @@ slow:
 	inode->i_fop = &ns_file_operations;
 	inode->i_private = ns;
 
-	dentry = d_alloc_pseudo(mnt->mnt_sb, &empty_name);
+	dentry = d_alloc_anon(mnt->mnt_sb);
 	if (!dentry) {
 		iput(inode);
 		return ERR_PTR(-ENOMEM);
 	}
 	d_instantiate(dentry, inode);
-	dentry->d_flags |= DCACHE_RCUACCESS;
 	dentry->d_fsdata = (void *)ns->ops;
 	d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
 	if (d) {

include/linux/dcache.h

@@ -176,7 +176,6 @@ struct dentry_operations {
       * typically using d_splice_alias. */
 
 #define DCACHE_REFERENCED		0x00000040 /* Recently used, don't discard. */
-#define DCACHE_RCUACCESS		0x00000080 /* Entry has ever been RCU-visible */
 
 #define DCACHE_CANT_MOUNT		0x00000100
 #define DCACHE_GENOCIDE			0x00000200
@@ -217,6 +216,7 @@ struct dentry_operations {
 
 #define DCACHE_PAR_LOOKUP		0x10000000 /* being looked up (with parent locked shared) */
 #define DCACHE_DENTRY_CURSOR		0x20000000
+#define DCACHE_NORCU			0x40000000 /* No RCU delay for freeing */
 
 extern seqlock_t rename_lock;
 

include/linux/mount.h

@@ -87,6 +87,8 @@ extern bool mnt_may_suid(struct vfsmount *mnt);
 
 struct path;
 extern struct vfsmount *clone_private_mount(const struct path *path);
+extern int __mnt_want_write(struct vfsmount *);
+extern void __mnt_drop_write(struct vfsmount *);
 
 struct file_system_type;
 extern struct vfsmount *fc_mount(struct fs_context *fc);

kernel/acct.c

@@ -227,7 +227,7 @@ static int acct_on(struct filename *pathname)
 		filp_close(file, NULL);
 		return PTR_ERR(internal);
 	}
-	err = mnt_want_write(internal);
+	err = __mnt_want_write(internal);
 	if (err) {
 		mntput(internal);
 		kfree(acct);
@@ -252,7 +252,7 @@ static int acct_on(struct filename *pathname)
 	old = xchg(&ns->bacct, &acct->pin);
 	mutex_unlock(&acct->lock);
 	pin_kill(old);
-	mnt_drop_write(mnt);
+	__mnt_drop_write(mnt);
 	mntput(mnt);
 	return 0;
 }