linux-kernel - Re: [PATCH -next 0/2] fs/epoll: loosen irq safety when possible

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Message-ID: <20180721173944.GV2494@hirez.programming.kicks-ass.net>
Date:   Sat, 21 Jul 2018 19:39:44 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, jbaron@...mai.com,
        viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next 0/2] fs/epoll: loosen irq safety when possible

On Sat, Jul 21, 2018 at 10:21:20AM -0700, Davidlohr Bueso wrote:
> On Fri, 20 Jul 2018, Andrew Morton wrote:
> 
> > We could open-code it locally.  Add a couple of
> > WARN_ON_ONCE(irqs_disabled())?  That might need re-benchmarking with
> > Xen but surely just reading the thing isn't too expensive?
> 
> We could also pass on the responsibility to lockdep and just use
> lockdep_assert_irqs_disabled(). But I guess that would be less effective
> than to just open code it in epoll without lockdep -- note that over 80
> places in the kernel do this.

The lockdep thing is relatively recent. I think someone proposed to go
replace a bunch of the open-coded ones at some point.