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Date: Mon, 18 May 2015 09:19:05 +0200
From: Gabriele Mazzotta <gabriele.mzt@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: juri.lelli@....com, mingo@...hat.com, linux-kernel@...r.kernel.org,
len.brown@...el.com, andrey.semin@...el.com
Subject: Re: Regression: turbostat stops working after suspend/resume cycle\
On Monday 18 May 2015 08:48:04 Peter Zijlstra wrote:
> On Sun, May 17, 2015 at 05:48:44PM +0200, Gabriele Mazzotta wrote:
> > Hi,
> >
> > I've recently noticed that if I suspend and resume my laptop, I can no
> > longer execute turbostat. This is what I get when I try to start it:
> > # turbostat
> > Could not migrate to CPU 1
> > turbostat: re-initialized with num_cpus 4
> > Could not migrate to CPU 1
> >
> > Since everything works as expected with v4.0, I ran a bisection and
> > found that commit 3c18d447b3b36a8d ("sched/core: Check for available
> > DL bandwidth in cpuset_cpu_inactive()") is the cause of the regression.
> >
> > I don't know if there's something else affected by that change, but
> > I can consistently reproduce the bug with turbostat.
>
>
> This should be fixed by the below commit which is already in Linus'
> tree.
Thank you for the quick reply. As I replied to Ingo's mail, which
arrived just a bit earlier than yours, yes, the commit here below fixes
the problem.
Thanks,
Gabriele
> ---
> commit 533445c6e53368569e50ab3fb712230c03d523f3
> Author: Omar Sandoval <osandov@...ndov.com>
> Date: Mon May 4 03:09:36 2015 -0700
>
> sched/core: Fix regression in cpuset_cpu_inactive() for suspend
>
> Commit 3c18d447b3b3 ("sched/core: Check for available DL bandwidth in
> cpuset_cpu_inactive()"), a SCHED_DEADLINE bugfix, had a logic error that
> caused a regression in setting a CPU inactive during suspend. I ran into
> this when a program was failing pthread_setaffinity_np() with EINVAL after
> a suspend+wake up.
>
> A simple reproducer:
>
> $ ./a.out
> sched_setaffinity: Success
> $ systemctl suspend
> $ ./a.out
> sched_setaffinity: Invalid argument
>
> ... where ./a.out is:
>
> #define _GNU_SOURCE
> #include <errno.h>
> #include <sched.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <unistd.h>
>
> int main(void)
> {
> long num_cores;
> cpu_set_t cpu_set;
> int ret;
>
> num_cores = sysconf(_SC_NPROCESSORS_ONLN);
> CPU_ZERO(&cpu_set);
> CPU_SET(num_cores - 1, &cpu_set);
> errno = 0;
> ret = sched_setaffinity(getpid(), sizeof(cpu_set), &cpu_set);
> perror("sched_setaffinity");
> return ret ? EXIT_FAILURE : EXIT_SUCCESS;
> }
>
> The mistake is that suspend is handled in the action ==
> CPU_DOWN_PREPARE_FROZEN case of the switch statement in
> cpuset_cpu_inactive().
>
> However, the commit in question masked out CPU_TASKS_FROZEN
> from the action, making this case dead.
>
> The fix is straightforward.
>
> Signed-off-by: Omar Sandoval <osandov@...ndov.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Juri Lelli <juri.lelli@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Fixes: 3c18d447b3b3 ("sched/core: Check for available DL bandwidth in cpuset_cpu_inactive()")
> Link: http://lkml.kernel.org/r/1cb5ecb3d6543c38cce5790387f336f54ec8e2bc.1430733960.git.osandov@osandov.com
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 34db9bf892a3..57bd333bc4ab 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6999,27 +6999,23 @@ static int cpuset_cpu_inactive(struct notifier_block *nfb, unsigned long action,
> unsigned long flags;
> long cpu = (long)hcpu;
> struct dl_bw *dl_b;
> + bool overflow;
> + int cpus;
>
> - switch (action & ~CPU_TASKS_FROZEN) {
> + switch (action) {
> case CPU_DOWN_PREPARE:
> - /* explicitly allow suspend */
> - if (!(action & CPU_TASKS_FROZEN)) {
> - bool overflow;
> - int cpus;
> -
> - rcu_read_lock_sched();
> - dl_b = dl_bw_of(cpu);
> + rcu_read_lock_sched();
> + dl_b = dl_bw_of(cpu);
>
> - raw_spin_lock_irqsave(&dl_b->lock, flags);
> - cpus = dl_bw_cpus(cpu);
> - overflow = __dl_overflow(dl_b, cpus, 0, 0);
> - raw_spin_unlock_irqrestore(&dl_b->lock, flags);
> + raw_spin_lock_irqsave(&dl_b->lock, flags);
> + cpus = dl_bw_cpus(cpu);
> + overflow = __dl_overflow(dl_b, cpus, 0, 0);
> + raw_spin_unlock_irqrestore(&dl_b->lock, flags);
>
> - rcu_read_unlock_sched();
> + rcu_read_unlock_sched();
>
> - if (overflow)
> - return notifier_from_errno(-EBUSY);
> - }
> + if (overflow)
> + return notifier_from_errno(-EBUSY);
> cpuset_update_active_cpus(false);
> break;
> case CPU_DOWN_PREPARE_FROZEN:
--
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