locking/locktorture: Fix NULL pointer dereference for cleanup paths

It has been found that paths that invoke cleanups through
lock_torture_cleanup() can trigger NULL pointer dereferencing
bugs during the statistics printing phase. This is mainly
because we should not be calling into statistics before we are
sure things have been set up correctly.

Specifically, early checks (and the need for handling this in
the cleanup call) only include parameter checks and basic
statistics allocation. Once we start write/read kthreads
we then consider the test as started. As such, update the function
in question to check for cxt.lwsa writer stats, if not set,
we either have a bogus parameter or -ENOMEM situation and
therefore only need to deal with general torture calls.

Reported-and-tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dhowells@redhat.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476038-27060-2-git-send-email-paulmck@linux.vnet.ibm.com
[ Improved the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/locking/locktorture.c

@@ -748,6 +748,15 @@ static void lock_torture_cleanup(void)
 	if (torture_cleanup_begin())
 		return;
 
+	/*
+	 * Indicates early cleanup, meaning that the test has not run,
+	 * such as when passing bogus args when loading the module. As
+	 * such, only perform the underlying torture-specific cleanups,
+	 * and avoid anything related to locktorture.
+	 */
+	if (!cxt.lwsa)
+		goto end;
+
 	if (writer_tasks) {
 		for (i = 0; i < cxt.nrealwriters_stress; i++)
 			torture_stop_kthread(lock_torture_writer,
@@ -776,6 +785,7 @@ static void lock_torture_cleanup(void)
 	else
 		lock_torture_print_module_parms(cxt.cur_ops,
 						"End of test: SUCCESS");
+end:
 	torture_cleanup_end();
 }
 
@@ -870,6 +880,7 @@ static int __init lock_torture_init(void)
 			VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
 			firsterr = -ENOMEM;
 			kfree(cxt.lwsa);
+			cxt.lwsa = NULL;
 			goto unwind;
 		}
 
@@ -878,6 +889,7 @@ static int __init lock_torture_init(void)
 			cxt.lrsa[i].n_lock_acquired = 0;
 		}
 	}
+
 	lock_torture_print_module_parms(cxt.cur_ops, "Start of test");
 
 	/* Prepare torture context. */