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Message-ID: <Yh/C7nnElPOL3G/k@hirez.programming.kicks-ass.net> Date: Wed, 2 Mar 2022 20:18:06 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Matthew Wilcox <willy@...radead.org> Cc: Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira <bristot@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 00/19] Enable -Wshadow=local for kernel/sched On Wed, Mar 02, 2022 at 06:43:57PM +0000, Matthew Wilcox wrote: > ie "__ret = freezable_schedule_timeout(__ret)" is supposed to refer to > the inner __ret, not the outer __ret. Which was the opposite of what > I thought was supposed to happen. > > We can fix this, of course. Something like ... > > #define ___wait_event_freezable_timeout(wq_head, condition, timeout, ret) \ > ___wait_event(wq_head, ___wait_cond_timeout(condition, ret), \ > TASK_INTERRUPTIBLE, 0, timeout, \ > ret = freezable_schedule_timeout(ret), ret) > > #define __wait_event_freezable_timeout(wq_head, condition, timeout) \ > ___wait_event_freezable_timeout(wq_head, condition, timeout, UNIQUE_ID) > > ... and now all the 'ret' refer to the thing that they look like they're > referring to. Right; so the trick is to make sure all ___wait_event() users will have a ret and then the inner ret can go away. The interruptible/timeout variants all already have a ret variable, but the unconditional things like wait_event() do not (which is where all the trouble started). By simply adding a ret variable, even to the variants without return value, the inner variable can go away and the shadowing goes away.
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