LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Dexuan Cui <decui@microsoft.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Rakib Mullick <rakib.mullick@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: RE: for_each_cpu() is buggy for UP kernel?
Date: Tue, 15 May 2018 20:10:22 +0000	[thread overview]
Message-ID: <KL1P15301MB0006432F17DE0DB6ABA80EDEBF930@KL1P15301MB0006.APCP153.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <CA+55aFziNcDmN=DT7efKYGU-AZC535GDVKh57bC7UHaFff3vRw@mail.gmail.com>

> From: Linus Torvalds <torvalds@linux-foundation.org>
> Sent: Tuesday, May 15, 2018 10:22
> To: Dexuan Cui <decui@microsoft.com>
> 
> On Mon, May 14, 2018 at 8:02 PM Dexuan Cui <decui@microsoft.com> wrote:
> 
> > If you're OK with the below fix (not tested yet), I'll submit a patch for it:
> 
> > --- a/kernel/time/tick-broadcast.c
> > +++ b/kernel/time/tick-broadcast.c
> > @@ -616,6 +616,10 @@ static void tick_handle_oneshot_broadcast(struct
> clock_event_device *dev)
> >          now = ktime_get();
> >          /* Find all expired events */
> >          for_each_cpu(cpu, tick_broadcast_oneshot_mask) {
> > +#ifndef CONFIG_SMP
> > +               if (cpumask_empty(tick_broadcast_oneshot_mask))
> > +                       break;
> > +#endif
> 
> I'm certainly ok with this. It's hacky, but maybe being explicitly hacky is
> good to "document" this gotcha.
> 
> And I really do agree that this special UP case is nasty nasty and much too
> subtle, and I hope that some day we won't care about UP at all, and maybe
> kill it, or maybe just make for_each_cpu() generate the extra code to have
> the actual same semantics as the SMP case.
> 
>                   Linus

Thanks! I submitted the patch just now: https://lkml.org/lkml/2018/5/15/866 

Thanks,
-- Dexuan

  reply	other threads:[~2018-05-15 20:10 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-09  6:24 Dexuan Cui
2018-05-09 23:20 ` Andrew Morton
2018-05-13 13:35   ` Thomas Gleixner
2018-05-13 18:21 ` Linus Torvalds
2018-05-14  7:28   ` Dmitry Vyukov
2018-05-15  3:02   ` Dexuan Cui
2018-05-15 17:21     ` Linus Torvalds
2018-05-15 20:10       ` Dexuan Cui [this message]
2018-05-15 19:52 ` [PATCH] tick/broadcast: Use for_each_cpu() specially on UP kernels Dexuan Cui
2018-05-15 20:48   ` [tip:timers/urgent] " tip-bot for Dexuan Cui

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=KL1P15301MB0006432F17DE0DB6ABA80EDEBF930@KL1P15301MB0006.APCP153.PROD.OUTLOOK.COM \
    --to=decui@microsoft.com \
    --cc=adobriyan@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=peterz@infradead.org \
    --cc=rakib.mullick@gmail.com \
    --cc=tglx@linutronix.de \
    --cc=torvalds@linux-foundation.org \
    --subject='RE: for_each_cpu() is buggy for UP kernel?' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).