Re: Regression: turbostat stops working after suspend/resume cycle\

[Peter Zijlstra <peterz@infradead.org>]

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.

---
commit 533445c6e53368569e50ab3fb712230c03d523f3
Author: Omar Sandoval <osandov@osandov.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@osandov.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Juri Lelli <juri.lelli@arm.com>
    Cc: Thomas Gleixner <tglx@linutronix.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@kernel.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: