Re: [PATCH v4] uart: fix race between uart_put_char() and uart_shutdown()

[Tycho Andersen]

On Thu, Jul 12, 2018 at 05:40:15PM +0200, Greg Kroah-Hartman wrote:
> On Thu, Jul 12, 2018 at 09:08:22AM -0600, Tycho Andersen wrote:
> > On Thu, Jul 12, 2018 at 05:04:38PM +0200, Greg Kroah-Hartman wrote:
> > > On Wed, Jul 11, 2018 at 10:07:44AM -0600, Tycho Andersen wrote:
> > > > +	if (uport)
> > > > +		spin_lock_irqsave(&uport->lock, flags);
> > > 
> > > That's the same thing as just calling uart_port_lock(), why aren't you
> > > doing that?
> > 
> > Because the compiler can't seem to "see" through the macros/ref calls,
> > and I get the warning I mentioned here if I use them:
> > 
> > https://lkml.org/lkml/2018/7/6/840
> 
> What horrible version of gcc are you using that give you that?  Don't
> open-code things just because of a broken compiler.

I've tried with both 7.3.0 and 5.4.0. I think the reason we see this
here but not elsewhere in the file is because there's an actual
function call (free_page()) in the critical section.

If we move that out, something like the below patch, it all works for
me.

Tycho