[PATCH] locktorture: Fix memory leak in param_set_cpumask()

[Wang Liang <wangliang74@huawei.com>]

When setting the locktorture module parameter 'bind_writers', the variable
'cpumask_var_t bind_writers' is allocated in param_set_cpumask(). But it
is not freed, when removing module or setting the parameter again.

Below kmemleak trace is seen for this issue:

unreferenced object 0xffff888100aabff8 (size 8):
  comm "bash", pid 323, jiffies 4295059233
  hex dump (first 8 bytes):
    07 00 00 00 00 00 00 00                          ........
  backtrace (crc ac50919):
    __kmalloc_node_noprof+0x2e5/0x420
    alloc_cpumask_var_node+0x1f/0x30
    param_set_cpumask+0x26/0xb0 [locktorture]
    param_attr_store+0x93/0x100
    module_attr_store+0x1b/0x30
    kernfs_fop_write_iter+0x114/0x1b0
    vfs_write+0x300/0x410
    ksys_write+0x60/0xd0
    do_syscall_64+0xa4/0x260
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

This issue can be reproduced by:
  insmod locktorture.ko
  echo 0-2 > /sys/module/locktorture/parameters/bind_writers
  rmmod locktorture

or:
  insmod locktorture.ko
  echo 0-2 > /sys/module/locktorture/parameters/bind_writers
  echo 0-2 > /sys/module/locktorture/parameters/bind_writers

The parameter 'bind_readers' also has the same problem. Free the memory
when removing module or setting the parameter.

Fixes: 73e341242483 ("locktorture: Add readers_bind and writers_bind module parameters")
Signed-off-by: Wang Liang <wangliang74@huawei.com>
---
 kernel/locking/locktorture.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index ce0362f0a871..cad80c050502 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -70,6 +70,9 @@ static int param_set_cpumask(const char *val, const struct kernel_param *kp)
 	int ret;
 	char *s;
 
+	free_cpumask_var(*cm_bind);
+	*cm_bind = NULL;
+
 	if (!alloc_cpumask_var(cm_bind, GFP_KERNEL)) {
 		s = "Out of memory";
 		ret = -ENOMEM;
@@ -1211,6 +1214,12 @@ static void lock_torture_cleanup(void)
 			cxt.cur_ops->exit();
 		cxt.init_called = false;
 	}
+
+	free_cpumask_var(bind_readers);
+	free_cpumask_var(bind_writers);
+	bind_readers = NULL;
+	bind_writers = NULL;
+
 	torture_cleanup_end();
 }
 
-- 
2.34.1