Merge branch 'work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull vfs dcache updates from Al Viro:
 "Part of this is what the trylock loop elimination series has turned
  into, part making d_move() preserve the parent (and thus the path) of
  victim, plus some general cleanups"

* 'work.dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (22 commits)
  d_genocide: move export to definition
  fold dentry_lock_for_move() into its sole caller and clean it up
  make non-exchanging __d_move() copy ->d_parent rather than swap them
  oprofilefs: don't oops on allocation failure
  lustre: get rid of pointless casts to struct dentry *
  debugfs_lookup(): switch to lookup_one_len_unlocked()
  fold lookup_real() into __lookup_hash()
  take out orphan externs (empty_string/slash_string)
  split d_path() and friends into a separate file
  dcache.c: trim includes
  fs/dcache: Avoid a try_lock loop in shrink_dentry_list()
  get rid of trylock loop around dentry_kill()
  handle move to LRU in retain_dentry()
  dput(): consolidate the "do we need to retain it?" into an inlined helper
  split the slow part of lock_parent() off
  now lock_parent() can't run into killed dentry
  get rid of trylock loop in locking dentries on shrink list
  d_delete(): get rid of trylock loop
  fs/dcache: Move dentry_kill() below lock_parent()
  fs/dcache: Remove stale comment from dentry_kill()
  ...

drivers/oprofile/oprofilefs.c

@@ -138,6 +138,9 @@ static int __oprofilefs_create_file(struct dentry *root, char const *name,
 	struct dentry *dentry;
 	struct inode *inode;
 
+	if (!root)
+		return -ENOMEM;
+
 	inode_lock(d_inode(root));
 	dentry = d_alloc_name(root, name);
 	if (!dentry) {

drivers/staging/lustre/lustre/llite/dcache.c

@@ -90,7 +90,7 @@ static int ll_dcompare(const struct dentry *dentry,
 	       d_count(dentry));
 
 	/* mountpoint is always valid */
-	if (d_mountpoint((struct dentry *)dentry))
+	if (d_mountpoint(dentry))
 		return 0;
 
 	if (d_lustre_invalid(dentry))
@@ -111,7 +111,7 @@ static int ll_ddelete(const struct dentry *de)
 	LASSERT(de);
 
 	CDEBUG(D_DENTRY, "%s dentry %pd (%p, parent %p, inode %p) %s%s\n",
-	       d_lustre_invalid((struct dentry *)de) ? "deleting" : "keeping",
+	       d_lustre_invalid(de) ? "deleting" : "keeping",
 	       de, de, de->d_parent, d_inode(de),
 	       d_unhashed(de) ? "" : "hashed,",
 	       list_empty(&de->d_subdirs) ? "" : "subdirs");
@@ -119,7 +119,7 @@ static int ll_ddelete(const struct dentry *de)
 	/* kernel >= 2.6.38 last refcount is decreased after this function. */
 	LASSERT(d_count(de) == 1);
 
-	if (d_lustre_invalid((struct dentry *)de))
+	if (d_lustre_invalid(de))
 		return 1;
 	return 0;
 }

fs/Makefile

@@ -11,7 +11,7 @@ obj-y :=	open.o read_write.o file_table.o super.o \
 		ioctl.o readdir.o select.o dcache.o inode.o \
 		attr.o bad_inode.o file.o filesystems.o namespace.o \
 		seq_file.o xattr.o libfs.o fs-writeback.o \
-		pnode.o splice.o sync.o utimes.o \
+		pnode.o splice.o sync.o utimes.o d_path.o \
 		stack.o fs_struct.o statfs.o fs_pin.o nsfs.o
 
 ifeq ($(CONFIG_BLOCK),y)

fs/d_path.c

+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/syscalls.h>
+#include <linux/export.h>
+#include <linux/uaccess.h>
+#include <linux/fs_struct.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/prefetch.h>
+#include "mount.h"
+
+static int prepend(char **buffer, int *buflen, const char *str, int namelen)
+{
+	*buflen -= namelen;
+	if (*buflen < 0)
+		return -ENAMETOOLONG;
+	*buffer -= namelen;
+	memcpy(*buffer, str, namelen);
+	return 0;
+}
+
+/**
+ * prepend_name - prepend a pathname in front of current buffer pointer
+ * @buffer: buffer pointer
+ * @buflen: allocated length of the buffer
+ * @name:   name string and length qstr structure
+ *
+ * With RCU path tracing, it may race with d_move(). Use READ_ONCE() to
+ * make sure that either the old or the new name pointer and length are
+ * fetched. However, there may be mismatch between length and pointer.
+ * The length cannot be trusted, we need to copy it byte-by-byte until
+ * the length is reached or a null byte is found. It also prepends "/" at
+ * the beginning of the name. The sequence number check at the caller will
+ * retry it again when a d_move() does happen. So any garbage in the buffer
+ * due to mismatched pointer and length will be discarded.
+ *
+ * Load acquire is needed to make sure that we see that terminating NUL.
+ */
+static int prepend_name(char **buffer, int *buflen, const struct qstr *name)
+{
+	const char *dname = smp_load_acquire(&name->name); /* ^^^ */
+	u32 dlen = READ_ONCE(name->len);
+	char *p;
+
+	*buflen -= dlen + 1;
+	if (*buflen < 0)
+		return -ENAMETOOLONG;
+	p = *buffer -= dlen + 1;
+	*p++ = '/';
+	while (dlen--) {
+		char c = *dname++;
+		if (!c)
+			break;
+		*p++ = c;
+	}
+	return 0;
+}
+
+/**
+ * prepend_path - Prepend path string to a buffer
+ * @path: the dentry/vfsmount to report
+ * @root: root vfsmnt/dentry
+ * @buffer: pointer to the end of the buffer
+ * @buflen: pointer to buffer length
+ *
+ * The function will first try to write out the pathname without taking any
+ * lock other than the RCU read lock to make sure that dentries won't go away.
+ * It only checks the sequence number of the global rename_lock as any change
+ * in the dentry's d_seq will be preceded by changes in the rename_lock
+ * sequence number. If the sequence number had been changed, it will restart
+ * the whole pathname back-tracing sequence again by taking the rename_lock.
+ * In this case, there is no need to take the RCU read lock as the recursive
+ * parent pointer references will keep the dentry chain alive as long as no
+ * rename operation is performed.
+ */
+static int prepend_path(const struct path *path,
+			const struct path *root,
+			char **buffer, int *buflen)
+{
+	struct dentry *dentry;
+	struct vfsmount *vfsmnt;
+	struct mount *mnt;
+	int error = 0;
+	unsigned seq, m_seq = 0;
+	char *bptr;
+	int blen;
+
+	rcu_read_lock();
+restart_mnt:
+	read_seqbegin_or_lock(&mount_lock, &m_seq);
+	seq = 0;
+	rcu_read_lock();
+restart:
+	bptr = *buffer;
+	blen = *buflen;
+	error = 0;
+	dentry = path->dentry;
+	vfsmnt = path->mnt;
+	mnt = real_mount(vfsmnt);
+	read_seqbegin_or_lock(&rename_lock, &seq);
+	while (dentry != root->dentry || vfsmnt != root->mnt) {
+		struct dentry * parent;
+
+		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
+			struct mount *parent = READ_ONCE(mnt->mnt_parent);
+			/* Escaped? */
+			if (dentry != vfsmnt->mnt_root) {
+				bptr = *buffer;
+				blen = *buflen;
+				error = 3;
+				break;
+			}
+			/* Global root? */
+			if (mnt != parent) {
+				dentry = READ_ONCE(mnt->mnt_mountpoint);
+				mnt = parent;
+				vfsmnt = &mnt->mnt;
+				continue;
+			}
+			if (!error)
+				error = is_mounted(vfsmnt) ? 1 : 2;
+			break;
+		}
+		parent = dentry->d_parent;
+		prefetch(parent);
+		error = prepend_name(&bptr, &blen, &dentry->d_name);
+		if (error)
+			break;
+
+		dentry = parent;
+	}
+	if (!(seq & 1))
+		rcu_read_unlock();
+	if (need_seqretry(&rename_lock, seq)) {
+		seq = 1;
+		goto restart;
+	}
+	done_seqretry(&rename_lock, seq);
+
+	if (!(m_seq & 1))
+		rcu_read_unlock();
+	if (need_seqretry(&mount_lock, m_seq)) {
+		m_seq = 1;
+		goto restart_mnt;
+	}
+	done_seqretry(&mount_lock, m_seq);
+
+	if (error >= 0 && bptr == *buffer) {
+		if (--blen < 0)
+			error = -ENAMETOOLONG;
+		else
+			*--bptr = '/';
+	}
+	*buffer = bptr;
+	*buflen = blen;
+	return error;
+}
+
+/**
+ * __d_path - return the path of a dentry
+ * @path: the dentry/vfsmount to report
+ * @root: root vfsmnt/dentry
+ * @buf: buffer to return value in
+ * @buflen: buffer length
+ *
+ * Convert a dentry into an ASCII path name.
+ *
+ * Returns a pointer into the buffer or an error code if the
+ * path was too long.
+ *
+ * "buflen" should be positive.
+ *
+ * If the path is not reachable from the supplied root, return %NULL.
+ */
+char *__d_path(const struct path *path,
+	       const struct path *root,
+	       char *buf, int buflen)
+{
+	char *res = buf + buflen;
+	int error;
+
+	prepend(&res, &buflen, "\0", 1);
+	error = prepend_path(path, root, &res, &buflen);
+
+	if (error < 0)
+		return ERR_PTR(error);
+	if (error > 0)
+		return NULL;
+	return res;
+}
+
+char *d_absolute_path(const struct path *path,
+	       char *buf, int buflen)
+{
+	struct path root = {};
+	char *res = buf + buflen;
+	int error;
+
+	prepend(&res, &buflen, "\0", 1);
+	error = prepend_path(path, &root, &res, &buflen);
+
+	if (error > 1)
+		error = -EINVAL;
+	if (error < 0)
+		return ERR_PTR(error);
+	return res;
+}
+
+/*
+ * same as __d_path but appends "(deleted)" for unlinked files.
+ */
+static int path_with_deleted(const struct path *path,
+			     const struct path *root,
+			     char **buf, int *buflen)
+{
+	prepend(buf, buflen, "\0", 1);
+	if (d_unlinked(path->dentry)) {
+		int error = prepend(buf, buflen, " (deleted)", 10);
+		if (error)
+			return error;
+	}
+
+	return prepend_path(path, root, buf, buflen);
+}
+
+static int prepend_unreachable(char **buffer, int *buflen)
+{
+	return prepend(buffer, buflen, "(unreachable)", 13);
+}
+
+static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
+{
+	unsigned seq;
+
+	do {
+		seq = read_seqcount_begin(&fs->seq);
+		*root = fs->root;
+	} while (read_seqcount_retry(&fs->seq, seq));
+}
+
+/**
+ * d_path - return the path of a dentry
+ * @path: path to report
+ * @buf: buffer to return value in
+ * @buflen: buffer length
+ *
+ * Convert a dentry into an ASCII path name. If the entry has been deleted
+ * the string " (deleted)" is appended. Note that this is ambiguous.
+ *
+ * Returns a pointer into the buffer or an error code if the path was
+ * too long. Note: Callers should use the returned pointer, not the passed
+ * in buffer, to use the name! The implementation often starts at an offset
+ * into the buffer, and may leave 0 bytes at the start.
+ *
+ * "buflen" should be positive.
+ */
+char *d_path(const struct path *path, char *buf, int buflen)
+{
+	char *res = buf + buflen;
+	struct path root;
+	int error;
+
+	/*
+	 * We have various synthetic filesystems that never get mounted.  On
+	 * these filesystems dentries are never used for lookup purposes, and
+	 * thus don't need to be hashed.  They also don't need a name until a
+	 * user wants to identify the object in /proc/pid/fd/.  The little hack
+	 * below allows us to generate a name for these objects on demand:
+	 *
+	 * Some pseudo inodes are mountable.  When they are mounted
+	 * path->dentry == path->mnt->mnt_root.  In that case don't call d_dname
+	 * and instead have d_path return the mounted path.
+	 */
+	if (path->dentry->d_op && path->dentry->d_op->d_dname &&
+	    (!IS_ROOT(path->dentry) || path->dentry != path->mnt->mnt_root))
+		return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
+
+	rcu_read_lock();
+	get_fs_root_rcu(current->fs, &root);
+	error = path_with_deleted(path, &root, &res, &buflen);
+	rcu_read_unlock();
+
+	if (error < 0)
+		res = ERR_PTR(error);
+	return res;
+}
+EXPORT_SYMBOL(d_path);
+
+/*
+ * Helper function for dentry_operations.d_dname() members
+ */
+char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
+			const char *fmt, ...)
+{
+	va_list args;
+	char temp[64];
+	int sz;
+
+	va_start(args, fmt);
+	sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;
+	va_end(args);
+
+	if (sz > sizeof(temp) || sz > buflen)
+		return ERR_PTR(-ENAMETOOLONG);
+
+	buffer += buflen - sz;
+	return memcpy(buffer, temp, sz);
+}
+
+char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
+{
+	char *end = buffer + buflen;
+	/* these dentries are never renamed, so d_lock is not needed */
+	if (prepend(&end, &buflen, " (deleted)", 11) ||
+	    prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len) ||
+	    prepend(&end, &buflen, "/", 1))  
+		end = ERR_PTR(-ENAMETOOLONG);
+	return end;
+}
+EXPORT_SYMBOL(simple_dname);
+
+/*
+ * Write full pathname from the root of the filesystem into the buffer.
+ */
+static char *__dentry_path(struct dentry *d, char *buf, int buflen)
+{
+	struct dentry *dentry;
+	char *end, *retval;
+	int len, seq = 0;
+	int error = 0;
+
+	if (buflen < 2)
+		goto Elong;
+
+	rcu_read_lock();
+restart:
+	dentry = d;
+	end = buf + buflen;
+	len = buflen;
+	prepend(&end, &len, "\0", 1);
+	/* Get '/' right */
+	retval = end-1;
+	*retval = '/';
+	read_seqbegin_or_lock(&rename_lock, &seq);
+	while (!IS_ROOT(dentry)) {
+		struct dentry *parent = dentry->d_parent;
+
+		prefetch(parent);
+		error = prepend_name(&end, &len, &dentry->d_name);
+		if (error)
+			break;
+
+		retval = end;
+		dentry = parent;
+	}
+	if (!(seq & 1))
+		rcu_read_unlock();
+	if (need_seqretry(&rename_lock, seq)) {
+		seq = 1;
+		goto restart;
+	}
+	done_seqretry(&rename_lock, seq);
+	if (error)
+		goto Elong;
+	return retval;
+Elong:
+	return ERR_PTR(-ENAMETOOLONG);
+}
+
+char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
+{
+	return __dentry_path(dentry, buf, buflen);
+}
+EXPORT_SYMBOL(dentry_path_raw);
+
+char *dentry_path(struct dentry *dentry, char *buf, int buflen)
+{
+	char *p = NULL;
+	char *retval;
+
+	if (d_unlinked(dentry)) {
+		p = buf + buflen;
+		if (prepend(&p, &buflen, "//deleted", 10) != 0)
+			goto Elong;
+		buflen++;
+	}
+	retval = __dentry_path(dentry, buf, buflen);
+	if (!IS_ERR(retval) && p)
+		*p = '/';	/* restore '/' overriden with '\0' */
+	return retval;
+Elong:
+	return ERR_PTR(-ENAMETOOLONG);
+}
+
+static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,
+				    struct path *pwd)
+{
+	unsigned seq;
+
+	do {
+		seq = read_seqcount_begin(&fs->seq);
+		*root = fs->root;
+		*pwd = fs->pwd;
+	} while (read_seqcount_retry(&fs->seq, seq));
+}
+
+/*
+ * NOTE! The user-level library version returns a
+ * character pointer. The kernel system call just
+ * returns the length of the buffer filled (which
+ * includes the ending '\0' character), or a negative
+ * error value. So libc would do something like
+ *
+ *	char *getcwd(char * buf, size_t size)
+ *	{
+ *		int retval;
+ *
+ *		retval = sys_getcwd(buf, size);
+ *		if (retval >= 0)
+ *			return buf;
+ *		errno = -retval;
+ *		return NULL;
+ *	}
+ */
+SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
+{
+	int error;
+	struct path pwd, root;
+	char *page = __getname();
+
+	if (!page)
+		return -ENOMEM;
+
+	rcu_read_lock();
+	get_fs_root_and_pwd_rcu(current->fs, &root, &pwd);
+
+	error = -ENOENT;
+	if (!d_unlinked(pwd.dentry)) {
+		unsigned long len;
+		char *cwd = page + PATH_MAX;
+		int buflen = PATH_MAX;
+
+		prepend(&cwd, &buflen, "\0", 1);
+		error = prepend_path(&pwd, &root, &cwd, &buflen);
+		rcu_read_unlock();
+
+		if (error < 0)
+			goto out;
+
+		/* Unreachable from current root */
+		if (error > 0) {
+			error = prepend_unreachable(&cwd, &buflen);
+			if (error)
+				goto out;
+		}
+
+		error = -ERANGE;
+		len = PATH_MAX + page - cwd;
+		if (len <= size) {
+			error = len;
+			if (copy_to_user(buf, cwd, len))
+				error = -EFAULT;
+		}
+	} else {
+		rcu_read_unlock();
+	}
+
+out:
+	__putname(page);
+	return error;
+}

fs/debugfs/inode.c

@@ -270,10 +270,7 @@ struct dentry *debugfs_lookup(const char *name, struct dentry *parent)
 	if (!parent)
 		parent = debugfs_mount->mnt_root;
 
-	inode_lock(d_inode(parent));
-	dentry = lookup_one_len(name, parent, strlen(name));
-	inode_unlock(d_inode(parent));
-
+	dentry = lookup_one_len_unlocked(name, parent, strlen(name));
 	if (IS_ERR(dentry))
 		return NULL;
 	if (!d_really_is_positive(dentry)) {

fs/namei.c

@@ -1474,43 +1474,36 @@ static struct dentry *lookup_dcache(const struct qstr *name,
 }
 
 /*
- * Call i_op->lookup on the dentry.  The dentry must be negative and
- * unhashed.
- *
- * dir->d_inode->i_mutex must be held
+ * 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.
  */
-static struct dentry *lookup_real(struct inode *dir, struct dentry *dentry,
-				  unsigned int flags)
-{
-	struct dentry *old;
-
-	/* Don't create child dentry for a dead directory. */
-	if (unlikely(IS_DEADDIR(dir))) {
-		dput(dentry);
-		return ERR_PTR(-ENOENT);
-	}
-
-	old = dir->i_op->lookup(dir, dentry, flags);
-	if (unlikely(old)) {
-		dput(dentry);
-		dentry = old;
-	}
-	return dentry;
-}
-
 static struct dentry *__lookup_hash(const struct qstr *name,
 		struct dentry *base, unsigned int flags)
 {
 	struct dentry *dentry = lookup_dcache(name, base, flags);
+	struct dentry *old;
+	struct inode *dir = base->d_inode;
 
 	if (dentry)
 		return dentry;
 
+	/* Don't create child dentry for a dead directory. */
+	if (unlikely(IS_DEADDIR(dir)))
+		return ERR_PTR(-ENOENT);
+
 	dentry = d_alloc(base, name);
 	if (unlikely(!dentry))
 		return ERR_PTR(-ENOMEM);
 
-	return lookup_real(base->d_inode, dentry, flags);
+	old = dir->i_op->lookup(dir, dentry, flags);
+	if (unlikely(old)) {
+		dput(dentry);
+		dentry = old;
+	}
+	return dentry;
 }
 
 static int lookup_fast(struct nameidata *nd,

include/linux/dcache.h

@@ -56,9 +56,7 @@ struct qstr {
 
 #define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
 
-extern const char empty_string[];
 extern const struct qstr empty_name;
-extern const char slash_string[];
 extern const struct qstr slash_name;
 
 struct dentry_stat_t {
@@ -361,7 +359,7 @@ static inline void dont_mount(struct dentry *dentry)
 
 extern void __d_lookup_done(struct dentry *);
 
-static inline int d_in_lookup(struct dentry *dentry)
+static inline int d_in_lookup(const struct dentry *dentry)
 {
 	return dentry->d_flags & DCACHE_PAR_LOOKUP;
 }
@@ -489,7 +487,7 @@ static inline bool d_really_is_positive(const struct dentry *dentry)
 	return dentry->d_inode != NULL;
 }
 
-static inline int simple_positive(struct dentry *dentry)
+static inline int simple_positive(const struct dentry *dentry)
 {
 	return d_really_is_positive(dentry) && !d_unhashed(dentry);
 }