Re: [PATCH] bdi: Fix another oops in wb_workfn()

[Linus Torvalds]

On Wed, Jun 13, 2018 at 9:21 AM Tetsuo Handa
<penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
>
> Since multiple addresses share bit_wait_table[256], isn't it possible that
> cgwb_start_shutdown() prematurely returns false due to wake_up_bit() by
> hash-conflicting addresses (i.e. not limited to clear_and_wake_up_bit() from
> wb_shutdown())? I think that we cannot be sure without confirming that
> test_bit(WB_shutting_down, &wb->state) == false after returning from schedule().

Right.

That's _always_ true, btw. Something else entirely could have woken
you up. TASK_UNINTERRUPTIBLE does not mean "nothing else wakes me", it
just means "_signals_ don't wake me".

So every single sleep always needs to be in a loop. Always.

              Linus