workqueue: fix parse_affn_scope() prefix matching bug

parse_affn_scope() uses strncasecmp() with the length of the candidate
name, which means it only checks if the input *starts with* a known
scope name.

Given that the upcoming diff will create "cache_shard" affinity scope,
writing "cache_shard" to a workqueue's affinity_scope sysfs attribute
always matches "cache" first, making it impossible to select
"cache_shard" via sysfs, so, this fix enable it to distinguish "cache"
and "cache_shard"

Fix by replacing the hand-rolled prefix matching loop with
sysfs_match_string(), which uses sysfs_streq() for exact matching
(modulo trailing newlines). Also add the missing const qualifier to
the wq_affn_names[] array declaration.

Note that sysfs_streq() is case-sensitive, unlike the previous
strncasecmp() approach. This is intentional and consistent with
how other sysfs attributes handle string matching in the kernel.

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 715a23d5348f5689ff2fb6608c1ae1793d6f1c2e..c1743b20a52449c084d58ae9a07a630134374e72 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -405,7 +405,7 @@ struct work_offq_data {
        u32                     flags;
 };
 
-static const char *wq_affn_names[WQ_AFFN_NR_TYPES] = {
+static const char * const wq_affn_names[WQ_AFFN_NR_TYPES] = {
        [WQ_AFFN_DFL]           = "default",
        [WQ_AFFN_CPU]           = "cpu",
        [WQ_AFFN_SMT]           = "smt",
@@ -7093,13 +7093,7 @@ int workqueue_unbound_housekeeping_update(const struct cpumask *hk)
 
 static int parse_affn_scope(const char *val)
 {
-       int i;
-
-       for (i = 0; i < ARRAY_SIZE(wq_affn_names); i++) {
-               if (!strncasecmp(val, wq_affn_names[i], strlen(wq_affn_names[i])))
-                       return i;
-       }
-       return -EINVAL;
+       return sysfs_match_string(wq_affn_names, val);
 }
 
 static int wq_affn_dfl_set(const char *val, const struct kernel_param *kp)