linux-kernel - Re: [PATCH] PM / wakeirq: Add wakeup name to dedicated wake irqs

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Date:   Tue, 20 Feb 2018 12:14:58 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Alan Stern <stern@...land.harvard.edu>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Tony Lindgren <tony@...mide.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Brian Norris <briannorris@...omium.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH] PM / wakeirq: Add wakeup name to dedicated wake irqs

On Friday, February 16, 2018 3:52:22 PM CET Andy Shevchenko wrote:
> On Fri, Feb 16, 2018 at 12:54 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> > On Fri, Feb 16, 2018 at 11:39 AM, Andy Shevchenko
> > <andy.shevchenko@...il.com> wrote:
> >> On Fri, Feb 16, 2018 at 11:14 AM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> >>> On Wed, Feb 14, 2018 at 12:23 PM, Andy Shevchenko
> >>> <andy.shevchenko@...il.com> wrote:
> 
> >>> IMO it is somewhat excessive to put the entire sprintf() under a raw
> >>> spinlock and it's not even necessary.
> >>
> >> It's a copy'n'paste of from the rest of functions there.
> >
> > Fair enough. :-)
> 
> >>> The value can change any time after you've dropped the lock and in
> >>> particular before the function returns, so why bother with locking?
> >>> desc will not go away from under you at that point anyway.
> >>
> >> IIRC descriptor's content might be changed, or descriptor itself might
> >> be gone (potential crash).
> >
> > No, desc cannot go away at this point AFAICS due to the kernfs
> > refcounting.  And the lock is *inside* of the desc object anyway, so
> > it doesn't help really against that.
> 
> Oh, indeed.
> 
> > The contents may change, but so what?
> >
> > Effectively, you read an int and reading an int is atomic.  It may
> > change after that, but the lock doesn't prevent it from changing.  It
> > only prevents the change from being applied to it before you drop the
> > lock, but why do you care?
> 
> So, with explanations above, perhaps we can produce the patch to
> remove those locks from the rest?

Well, I guess so.

I'm not the maintainer of that code, however. :-)