lockd: convert nsm_mutex to a spinlock
There's no reason for a mutex here, except to allow an allocation under
the lock, which we can avoid with the usual trick of preallocating
memory for the new object and freeing it if it turns out to be
unnecessary.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/fs/lockd/host.c b/fs/lockd/host.c
index de0ffb6..c785479 100644
--- a/fs/lockd/host.c
+++ b/fs/lockd/host.c
@@ -457,7 +457,7 @@
* Manage NSM handles
*/
static LIST_HEAD(nsm_handles);
-static DEFINE_MUTEX(nsm_mutex);
+static DEFINE_SPINLOCK(nsm_lock);
static struct nsm_handle *
__nsm_find(const struct sockaddr_in *sin,
@@ -479,7 +479,8 @@
return NULL;
}
- mutex_lock(&nsm_mutex);
+retry:
+ spin_lock(&nsm_lock);
list_for_each_entry(pos, &nsm_handles, sm_link) {
if (hostname && nsm_use_hostnames) {
@@ -489,28 +490,32 @@
} else if (!nlm_cmp_addr(&pos->sm_addr, sin))
continue;
atomic_inc(&pos->sm_count);
+ kfree(nsm);
nsm = pos;
- goto out;
+ goto found;
}
+ if (nsm) {
+ list_add(&nsm->sm_link, &nsm_handles);
+ goto found;
+ }
+ spin_unlock(&nsm_lock);
- if (!create) {
- nsm = NULL;
- goto out;
- }
+ if (!create)
+ return NULL;
nsm = kzalloc(sizeof(*nsm) + hostname_len + 1, GFP_KERNEL);
if (nsm == NULL)
- goto out;
+ return NULL;
+
nsm->sm_addr = *sin;
nsm->sm_name = (char *) (nsm + 1);
memcpy(nsm->sm_name, hostname, hostname_len);
nsm->sm_name[hostname_len] = '\0';
atomic_set(&nsm->sm_count, 1);
+ goto retry;
- list_add(&nsm->sm_link, &nsm_handles);
-
-out:
- mutex_unlock(&nsm_mutex);
+found:
+ spin_unlock(&nsm_lock);
return nsm;
}
@@ -529,10 +534,9 @@
{
if (!nsm)
return;
- mutex_lock(&nsm_mutex);
- if (atomic_dec_and_test(&nsm->sm_count)) {
+ if (atomic_dec_and_lock(&nsm->sm_count, &nsm_lock)) {
list_del(&nsm->sm_link);
+ spin_unlock(&nsm_lock);
kfree(nsm);
}
- mutex_unlock(&nsm_mutex);
}