workqueue: Try to catch flush_work() without INIT_WORK().

syzbot found a flush_work() caller who forgot to call INIT_WORK()
because that work_struct was allocated by kzalloc() [1]. But the message

  INFO: trying to register non-static key.
  the code is fine but needs lockdep annotation.
  turning off the locking correctness validator.

by lock_map_acquire() is failing to tell that INIT_WORK() is missing.

Since flush_work() without INIT_WORK() is a bug, and INIT_WORK() should
set ->func field to non-zero, let's warn if ->func field is zero.

[1] https://syzkaller.appspot.com/bug?id=a5954455fcfa51c29ca2ab55b203076337e1c770

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 392be4b252f6..a503ad9d0aec 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2908,6 +2908,9 @@ static bool __flush_work(struct work_struct *work, bool from_cancel)
         if (WARN_ON(!wq_online))
                 return false;
 
+        if (WARN_ON(!work->func))
+                return false;
+
         if (!from_cancel) {
                 lock_map_acquire(&work->lockdep_map);
                 lock_map_release(&work->lockdep_map);