zfs_allow_log_key TSD key: re-work the handling of this key's value

via saved_poolname.  Build saved_poolname in a local array and then
use strdup() to save it when necessary.  The code previously allocated
space for the TSD value with kmem_alloc which doesn't seemt to play well
(accounting-wise) with strfree() (which is the function used to free
the value later on).

module/zfs/zfs_ioctl.c

@@ -5705,7 +5705,7 @@ zfsdev_ioctl(struct file *filp, unsigned cmd, unsigned long arg)
 	uint_t vecnum;
 	int error, rc, len, flag = 0;
 	const zfs_ioc_vec_t *vec;
-	char *saved_poolname = NULL;
+	char saved_poolname[MAXNAMELEN];
 	nvlist_t *innvl = NULL;
 
 	vecnum = cmd - ZFS_IOC_FIRST;
@@ -5763,9 +5763,9 @@ zfsdev_ioctl(struct file *filp, unsigned cmd, unsigned long arg)
 		goto out;
 
 	/* legacy ioctls can modify zc_name */
-	len = strcspn(zc->zc_name, "/@") + 1;
-	saved_poolname = kmem_alloc(len, KM_SLEEP);
-	(void) strlcpy(saved_poolname, zc->zc_name, len);
+	(void) strlcpy(saved_poolname, zc->zc_name, sizeof(saved_poolname));
+	len = strcspn(saved_poolname, "/@") + 1;
+	saved_poolname[len] = '\0';
 
 	if (vec->zvec_func != NULL) {
 		nvlist_t *outnvl;
@@ -5830,10 +5830,7 @@ zfsdev_ioctl(struct file *filp, unsigned cmd, unsigned long arg)
 		char *s = tsd_get(zfs_allow_log_key);
 		if (s != NULL)
 			strfree(s);
-		(void) tsd_set(zfs_allow_log_key, saved_poolname);
-	} else {
-		if (saved_poolname != NULL)
-			strfree(saved_poolname);
+		(void) tsd_set(zfs_allow_log_key, strdup(saved_poolname));
 	}
 
 	kmem_free(zc, sizeof (zfs_cmd_t));