Allow d_manage() to be used in RCU-walk mode

Allow d_manage() to be called from pathwalk when it is in RCU-walk mode as well as when it is in Ref-walk mode. This permits __follow_mount_rcu() to call d_manage() directly. d_manage() needs a parameter to indicate that it is in RCU-walk mode as it isn't allowed to sleep if in that mode (but should return -ECHILD instead). autofs4_d_manage() can then be set to retain RCU-walk mode if the daemon accesses it and otherwise request dropping back to ref-walk mode. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Allow d_manage() to be used in RCU-walk mode
Allow d_manage() to be called from pathwalk when it is in RCU-walk mode as well as when it is in Ref-walk mode. This permits __follow_mount_rcu() to call d_manage() directly. d_manage() needs a parameter to indicate that it is in RCU-walk mode as it isn't allowed to sleep if in that mode (but should return -ECHILD instead). autofs4_d_manage() can then be set to retain RCU-walk mode if the daemon accesses it and otherwise request dropping back to ref-walk mode. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
David Howells · Al Viro
1 parent 87556ef199
Showing 5 changed files with 22 additions and 12 deletions Side-by-side Diff
Documentation/filesystems/Locking
Documentation/filesystems/vfs.txt
fs/autofs4/root.c
fs/namei.c
include/linux/dcache.h
@@ -32,7 +32,7 @@
 d_iput:		no		no		yes		no
 d_dname:	no		no		no		no
 d_automount:	no		no		yes		no
-d_manage:	no		no		yes		no
+d_manage:	no		no		yes (ref-walk)	maybe
  
 --------------------------- inode_operations --------------------------- 
 prototypes:
@@ -865,7 +865,7 @@
 	void (*d_iput)(struct dentry *, struct inode *);
 	char *(*d_dname)(struct dentry *, char *, int);
 	struct vfsmount *(*d_automount)(struct path *);
-	int (*d_manage)(struct dentry *, bool);
+	int (*d_manage)(struct dentry *, bool, bool);
 };
  
   d_revalidate: called when the VFS needs to revalidate a dentry. This
@@ -959,6 +959,11 @@
 	If the 'mounting_here' parameter is true, then namespace_sem is being
 	held by the caller and the function should not initiate any mounts or
 	unmounts that it will then wait for.
+
+	If the 'rcu_walk' parameter is true, then the caller is doing a
+	pathwalk in RCU-walk mode.  Sleeping is not permitted in this mode,
+	and the caller can be asked to leave it and call again by returing
+	-ECHILD.
  
 	This function is only used if DCACHE_MANAGE_TRANSIT is set on the
 	dentry being transited from.
@@ -36,7 +36,7 @@
 static int autofs4_dir_open(struct inode *inode, struct file *file);
 static struct dentry *autofs4_lookup(struct inode *,struct dentry *, struct nameidata *);
 static struct vfsmount *autofs4_d_automount(struct path *);
-static int autofs4_d_manage(struct dentry *, bool);
+static int autofs4_d_manage(struct dentry *, bool, bool);
  
 const struct file_operations autofs4_root_operations = {
 	.open		= dcache_dir_open,
@@ -450,7 +450,7 @@
 	return NULL;
 }
  
-int autofs4_d_manage(struct dentry *dentry, bool mounting_here)
+int autofs4_d_manage(struct dentry *dentry, bool mounting_here, bool rcu_walk)
 {
 	struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
  
@@ -463,6 +463,10 @@
 			return -EISDIR;
 		return 0;
 	}
+
+	/* We need to sleep, so we need pathwalk to be in ref-mode */
+	if (rcu_walk)
+		return -ECHILD;
  
 	/* Wait for pending expires */
 	do_expire_wait(dentry);
@@ -987,7 +987,8 @@
 		if (managed & DCACHE_MANAGE_TRANSIT) {
 			BUG_ON(!path->dentry->d_op);
 			BUG_ON(!path->dentry->d_op->d_manage);
-			ret = path->dentry->d_op->d_manage(path->dentry, false);
+			ret = path->dentry->d_op->d_manage(path->dentry,
+							   false, false);
 			if (ret < 0)
 				return ret == -EISDIR ? 0 : ret;
 		}
  
@@ -1048,13 +1049,12 @@
 static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
 			       struct inode **inode, bool reverse_transit)
 {
-	unsigned abort_mask =
-		reverse_transit ? 0 : DCACHE_MANAGE_TRANSIT;
-
 	while (d_mountpoint(path->dentry)) {
 		struct vfsmount *mounted;
-		if (path->dentry->d_flags & abort_mask)
-			return true;
+		if (unlikely(path->dentry->d_flags & DCACHE_MANAGE_TRANSIT) &&
+		    !reverse_transit &&
+		    path->dentry->d_op->d_manage(path->dentry, false, true) < 0)
+			return false;
 		mounted = __lookup_mnt(path->mnt, path->dentry, 1);
 		if (!mounted)
 			break;
@@ -1132,7 +1132,8 @@
 		if (managed & DCACHE_MANAGE_TRANSIT) {
 			BUG_ON(!path->dentry->d_op);
 			BUG_ON(!path->dentry->d_op->d_manage);
-			ret = path->dentry->d_op->d_manage(path->dentry, mounting_here);
+			ret = path->dentry->d_op->d_manage(
+				path->dentry, mounting_here, false);
 			if (ret < 0)
 				return ret == -EISDIR ? 0 : ret;
 		}
@@ -168,7 +168,7 @@
 	void (*d_iput)(struct dentry *, struct inode *);
 	char *(*d_dname)(struct dentry *, char *, int);
 	struct vfsmount *(*d_automount)(struct path *);
-	int (*d_manage)(struct dentry *, bool);
+	int (*d_manage)(struct dentry *, bool, bool);
 } ____cacheline_aligned;
  
 /*
...	...	@@ -32,7 +32,7 @@
32	32	d_iput: no no yes no
33	33	d_dname: no no no no
34	34	d_automount: no no yes no
35		-d_manage: no no yes no
	35	+d_manage: no no yes (ref-walk) maybe
36	36
37	37	--------------------------- inode_operations ---------------------------
38	38	prototypes:
...	...	@@ -865,7 +865,7 @@
865	865	void (d_iput)(struct dentry , struct inode *);
866	866	char (d_dname)(struct dentry , char , int);
867	867	struct vfsmount (d_automount)(struct path *);
868		- int (d_manage)(struct dentry , bool);
	868	+ int (d_manage)(struct dentry , bool, bool);
869	869	};
870	870
871	871	d_revalidate: called when the VFS needs to revalidate a dentry. This
...	...	@@ -959,6 +959,11 @@
959	959	If the 'mounting_here' parameter is true, then namespace_sem is being
960	960	held by the caller and the function should not initiate any mounts or
961	961	unmounts that it will then wait for.
	962	+
	963	+ If the 'rcu_walk' parameter is true, then the caller is doing a
	964	+ pathwalk in RCU-walk mode. Sleeping is not permitted in this mode,
	965	+ and the caller can be asked to leave it and call again by returing
	966	+ -ECHILD.
962	967
963	968	This function is only used if DCACHE_MANAGE_TRANSIT is set on the
964	969	dentry being transited from.
...	...	@@ -36,7 +36,7 @@
36	36	static int autofs4_dir_open(struct inode inode, struct file file);
37	37	static struct dentry autofs4_lookup(struct inode ,struct dentry , struct nameidata );
38	38	static struct vfsmount autofs4_d_automount(struct path );
39		-static int autofs4_d_manage(struct dentry *, bool);
	39	+static int autofs4_d_manage(struct dentry *, bool, bool);
40	40
41	41	const struct file_operations autofs4_root_operations = {
42	42	.open = dcache_dir_open,
...	...	@@ -450,7 +450,7 @@
450	450	return NULL;
451	451	}
452	452
453		-int autofs4_d_manage(struct dentry *dentry, bool mounting_here)
	453	+int autofs4_d_manage(struct dentry *dentry, bool mounting_here, bool rcu_walk)
454	454	{
455	455	struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
456	456
...	...	@@ -463,6 +463,10 @@
463	463	return -EISDIR;
464	464	return 0;
465	465	}
	466	+
	467	+ /* We need to sleep, so we need pathwalk to be in ref-mode */
	468	+ if (rcu_walk)
	469	+ return -ECHILD;
466	470
467	471	/* Wait for pending expires */
468	472	do_expire_wait(dentry);
...	...	@@ -987,7 +987,8 @@
987	987	if (managed & DCACHE_MANAGE_TRANSIT) {
988	988	BUG_ON(!path->dentry->d_op);
989	989	BUG_ON(!path->dentry->d_op->d_manage);
990		- ret = path->dentry->d_op->d_manage(path->dentry, false);
	990	+ ret = path->dentry->d_op->d_manage(path->dentry,
	991	+ false, false);
991	992	if (ret < 0)
992	993	return ret == -EISDIR ? 0 : ret;
993	994	}
994	995
...	...	@@ -1048,13 +1049,12 @@
1048	1049	static bool __follow_mount_rcu(struct nameidata nd, struct path path,
1049	1050	struct inode **inode, bool reverse_transit)
1050	1051	{
1051		- unsigned abort_mask =
1052		- reverse_transit ? 0 : DCACHE_MANAGE_TRANSIT;
1053		-
1054	1052	while (d_mountpoint(path->dentry)) {
1055	1053	struct vfsmount *mounted;
1056		- if (path->dentry->d_flags & abort_mask)
1057		- return true;
	1054	+ if (unlikely(path->dentry->d_flags & DCACHE_MANAGE_TRANSIT) &&
	1055	+ !reverse_transit &&
	1056	+ path->dentry->d_op->d_manage(path->dentry, false, true) < 0)
	1057	+ return false;
1058	1058	mounted = __lookup_mnt(path->mnt, path->dentry, 1);
1059	1059	if (!mounted)
1060	1060	break;
...	...	@@ -1132,7 +1132,8 @@
1132	1132	if (managed & DCACHE_MANAGE_TRANSIT) {
1133	1133	BUG_ON(!path->dentry->d_op);
1134	1134	BUG_ON(!path->dentry->d_op->d_manage);
1135		- ret = path->dentry->d_op->d_manage(path->dentry, mounting_here);
	1135	+ ret = path->dentry->d_op->d_manage(
	1136	+ path->dentry, mounting_here, false);
1136	1137	if (ret < 0)
1137	1138	return ret == -EISDIR ? 0 : ret;
1138	1139	}
...	...	@@ -168,7 +168,7 @@
168	168	void (d_iput)(struct dentry , struct inode *);
169	169	char (d_dname)(struct dentry , char , int);
170	170	struct vfsmount (d_automount)(struct path *);
171		- int (d_manage)(struct dentry , bool);
	171	+ int (d_manage)(struct dentry , bool, bool);
172	172	} ____cacheline_aligned;
173	173
174	174	/*