kernfs: make kernfs_walk_ns() use kernfs_pr_cont_buf[]

kernfs_walk_ns() uses a static path_buf[PATH_MAX] to separate out path
components.  Keeping around the 4k buffer just for kernfs_walk_ns() is
wasteful.  This patch makes it piggyback on kernfs_pr_cont_buf[]
instead.  This requires kernfs_walk_ns() to hold kernfs_rename_lock.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 14 insertions, 5 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 996b7742c90b..118d033bcbbc 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -691,15 +691,22 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
                                           const unsigned char *path,
                                           const void *ns)
 {
-        static char path_buf[PATH_MAX]; /* protected by kernfs_mutex */
-        size_t len = strlcpy(path_buf, path, PATH_MAX);
-        char *p = path_buf;
-        char *name;
+        size_t len;
+        char *p, *name;
 
         lockdep_assert_held(&kernfs_mutex);
 
-        if (len >= PATH_MAX)
+        /* grab kernfs_rename_lock to piggy back on kernfs_pr_cont_buf */
+        spin_lock_irq(&kernfs_rename_lock);
+
+        len = strlcpy(kernfs_pr_cont_buf, path, sizeof(kernfs_pr_cont_buf));
+
+        if (len >= sizeof(kernfs_pr_cont_buf)) {
+                spin_unlock_irq(&kernfs_rename_lock);
                 return NULL;
+        }
+
+        p = kernfs_pr_cont_buf;
 
         while ((name = strsep(&p, "/")) && parent) {
                 if (*name == '\0')
@@ -707,6 +714,8 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
                 parent = kernfs_find_ns(parent, name, ns);
         }
 
+        spin_unlock_irq(&kernfs_rename_lock);
+
         return parent;
 }