linux-kernel - Re: [PATCH 2/2] Introduce __cond_lock

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Date:   Thu, 21 Dec 2017 17:10:00 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        linux-mm@...ck.org, Josh Triplett <josh@...htriplett.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>
Subject: Re: [PATCH 2/2] Introduce __cond_lock_err

On Thu, Dec 21, 2017 at 02:48:10PM -0700, Ross Zwisler wrote:
> > +++ b/include/linux/compiler_types.h
> > @@ -16,6 +16,7 @@
> >  # define __acquire(x)	__context__(x,1)
> >  # define __release(x)	__context__(x,-1)
> >  # define __cond_lock(x,c)	((c) ? ({ __acquire(x); 1; }) : 0)
> > +# define __cond_lock_err(x,c)	((c) ? 1 : ({ __acquire(x); 0; }))
> 					       ^
> I think we actually want this to return c here ^
> 
> The old code saved off the actual return value from __follow_pte_pmd() (say,
> -EINVAL) in 'res', and that was what was returned on error from both
> follow_pte_pmd() and follow_pte().  The value of 1 returned by __cond_lock()
> was just discarded (after we cast it to void for some reason).
> 
> With this new code we actually return the value from __cond_lock_err(), which
> means that instead of returning -EINVAL, we'll return 1 on error.

Yes, but this define is only #if __CHECKER__, so it doesn't matter what we
return as this code will never run.

That said, if sparse supports the GNU syntax of ?: then I have no
objection to doing that.