vfs: make d_path() get the root path under RCU

[platform/adaptation/renesas_rcar/renesas_kernel.git] / fs / dcache.c

diff --git a/fs/dcache.c b/fs/dcache.c
index 4d9df3c..dddc67f 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -90,8 +90,8 @@ static struct kmem_cache *dentry_cache __read_mostly;
 
 /**
  * read_seqbegin_or_lock - begin a sequence number check or locking block
- * lock: sequence lock
- * seq : sequence number to be checked
+ * @lock: sequence lock
+ * @seq : sequence number to be checked
  *
  * First try it once optimistically without taking the lock. If that fails,
  * take the lock. The sequence number is also used as a marker for deciding
@@ -103,7 +103,7 @@ static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
        if (!(*seq & 1))        /* Even */
                *seq = read_seqbegin(lock);
        else                    /* Odd */
-               write_seqlock(lock);
+               read_seqlock_excl(lock);
 }
 
 static inline int need_seqretry(seqlock_t *lock, int seq)
@@ -114,7 +114,7 @@ static inline int need_seqretry(seqlock_t *lock, int seq)
 static inline void done_seqretry(seqlock_t *lock, int seq)
 {
        if (seq & 1)
-               write_sequnlock(lock);
+               read_sequnlock_excl(lock);
 }
 
 /*
@@ -2673,9 +2673,9 @@ static int prepend(char **buffer, int *buflen, const char *str, int namelen)
 
 /**
  * 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
+ * @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 ACCESS_ONCE() to
  * make sure that either the old or the new name pointer and length are
@@ -2713,14 +2713,15 @@ static int prepend_name(char **buffer, int *buflen, struct qstr *name)
  * @buffer: pointer to the end of the buffer
  * @buflen: pointer to buffer length
  *
- * The function tries 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 change, it will restart the whole
- * pathname back-tracing sequence again. It performs a total of 3 trials of
- * lockless back-tracing sequences before falling back to take the
- * rename_lock.
+ * 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,
@@ -2868,6 +2869,16 @@ 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
@@ -2900,13 +2911,15 @@ char *d_path(const struct path *path, char *buf, int buflen)
        if (path->dentry->d_op && path->dentry->d_op->d_dname)
                return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
 
-       get_fs_root(current->fs, &root);
+       rcu_read_lock();
+       get_fs_root_rcu(current->fs, &root);
        br_read_lock(&vfsmount_lock);
        error = path_with_deleted(path, &root, &res, &buflen);
        br_read_unlock(&vfsmount_lock);
+       rcu_read_unlock();
+
        if (error < 0)
                res = ERR_PTR(error);
-       path_put(&root);
        return res;
 }
 EXPORT_SYMBOL(d_path);
@@ -3014,6 +3027,18 @@ 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
@@ -3036,23 +3061,25 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
 {
        int error;
        struct path pwd, root;
-       char *page = (char *) __get_free_page(GFP_USER);
+       char *page = __getname();
 
        if (!page)
                return -ENOMEM;
 
-       get_fs_root_and_pwd(current->fs, &root, &pwd);
+       rcu_read_lock();
+       get_fs_root_and_pwd_rcu(current->fs, &root, &pwd);
 
        error = -ENOENT;
        br_read_lock(&vfsmount_lock);
        if (!d_unlinked(pwd.dentry)) {
                unsigned long len;
-               char *cwd = page + PAGE_SIZE;
-               int buflen = PAGE_SIZE;
+               char *cwd = page + PATH_MAX;
+               int buflen = PATH_MAX;
 
                prepend(&cwd, &buflen, "\0", 1);
                error = prepend_path(&pwd, &root, &cwd, &buflen);
                br_read_unlock(&vfsmount_lock);
+               rcu_read_unlock();
 
                if (error < 0)
                        goto out;
@@ -3065,7 +3092,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
                }
 
                error = -ERANGE;
-               len = PAGE_SIZE + page - cwd;
+               len = PATH_MAX + page - cwd;
                if (len <= size) {
                        error = len;
                        if (copy_to_user(buf, cwd, len))
@@ -3073,12 +3100,11 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
                }
        } else {
                br_read_unlock(&vfsmount_lock);
+               rcu_read_unlock();
        }
 
 out:
-       path_put(&pwd);
-       path_put(&root);
-       free_page((unsigned long) page);
+       __putname(page);
        return error;
 }