From a20d46a06cc45d57ecdd62edc1b1354126984c9c Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Thu, 22 Oct 2015 09:03:53 +1100 Subject: [PATCH] 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 Cc: Greg KH Signed-off-by: Andrew Morton --- lib/kobject.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) diff --git a/lib/kobject.c b/lib/kobject.c index 3e3a5c3cb330..fee2fd950306 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); @@ -632,7 +646,7 @@ 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); } } -- 2.39.5