lib/kobject.c: use kvasprintf_const for formatting ->name

Sometimes kobject_set_name_vargs is called with a format string conaining
no %, or a format string of precisely "%s", where the single vararg
happens to point to .rodata.  kvasprintf_const detects these cases for us
and returns a copy of that pointer instead of duplicating the string, thus
saving some run-time memory.  Otherwise, it falls back to kvasprintf.  We
just need to always deallocate ->name using kfree_const.

Unfortunately, the dance we need to do to perform the '/' -> '!'
sanitization makes the resulting code rather ugly.

I instrumented kstrdup_const to provide some statistics on the memory
saved, and for me this gave an additional ~14KB after boot (306KB was
already saved; this patch bumped that to 320KB).  I have
KMALLOC_SHIFT_LOW==3, and since 80% of the kvasprintf_const hits were
satisfied by an 8-byte allocation, the 14K would roughly be quadrupled
when KMALLOC_SHIFT_LOW==5.  Whether these numbers are sufficient to
justify the ugliness I'll leave to others to decide.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 22 insertions, 8 deletions

diff --git a/lib/kobject.c b/lib/kobject.c
index 055407746266..7cbccd2b4c72 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -257,18 +257,32 @@ static int kobject_add_internal(struct kobject *kobj)
 int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,
                                   va_list vargs)
 {
-        char *s;
+        const char *s;
 
         if (kobj->name && !fmt)
                 return 0;
 
-        s = kvasprintf(GFP_KERNEL, fmt, vargs);
+        s = kvasprintf_const(GFP_KERNEL, fmt, vargs);
         if (!s)
                 return -ENOMEM;
 
-        /* ewww... some of these buggers have '/' in the name ... */
-        strreplace(s, '/', '!');
-        kfree(kobj->name);
+        /*
+         * ewww... some of these buggers have '/' in the name ... If
+         * that's the case, we need to make sure we have an actual
+         * allocated copy to modify, since kvasprintf_const may have
+         * returned something from .rodata.
+         */
+        if (strchr(s, '/')) {
+                char *t;
+
+                t = kstrdup(s, GFP_KERNEL);
+                kfree_const(s);
+                if (!t)
+                        return -ENOMEM;
+                strreplace(t, '/', '!');
+                s = t;
+        }
+        kfree_const(kobj->name);
         kobj->name = s;
 
         return 0;
@@ -466,7 +480,7 @@ int kobject_rename(struct kobject *kobj, const char *new_name)
         envp[0] = devpath_string;
         envp[1] = NULL;
 
-        name = dup_name = kstrdup(new_name, GFP_KERNEL);
+        name = dup_name = kstrdup_const(new_name, GFP_KERNEL);
         if (!name) {
                 error = -ENOMEM;
                 goto out;
@@ -486,7 +500,7 @@ int kobject_rename(struct kobject *kobj, const char *new_name)
         kobject_uevent_env(kobj, KOBJ_MOVE, envp);
 
 out:
-        kfree(dup_name);
+        kfree_const(dup_name);
         kfree(devpath_string);
         kfree(devpath);
         kobject_put(kobj);
@@ -634,7 +648,7 @@ static void kobject_cleanup(struct kobject *kobj)
         /* free name if we allocated it */
         if (name) {
                 pr_debug("kobject: '%s': free name\n", name);
-                kfree(name);
+                kfree_const(name);
         }
 }