Re: [tip:locking/core] sched/wait: Fix signal handling in bit wait helpers

[Oleg Nesterov <oleg@redhat.com>]

On 12/11, Peter Zijlstra wrote:
>
> On Fri, Dec 11, 2015 at 03:30:33AM -0800, Paul Turner wrote:
>
> > > Blergh, all I've managed to far is to confuse myself further. Even
> > > something like the original (+- the EINTR) should work when we consider
> > > the looping, even when mixed with an occasional spurious wakeup.
> > >
> > >
> > > int bit_wait()
> > > {
> > >         if (signal_pending_state(current->state, current))
> > >                 return -EINTR;
> > >         schedule();
> > > }
>
> So I asked Vladimir to test that (simply changing the return from 1 to
> -EINTR) and it made his fail much less likely but it still failed in the
> same way.
>
> So I'm fairly sure I'm still missing something :/

Same here...

Yes, "return 1" in bit_wait_io() doesn't look right. For example
do_generic_file_read() can wrongly return if lock_page_killable() returns
this error code. But I fail to understand how this can read to rcu-stall.

Oleg.