linux-kernel - [PATCH] sched/core: fix regression in cpuset_cpu

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Message-Id: <1cb5ecb3d6543c38cce5790387f336f54ec8e2bc.1430733960.git.osandov@osandov.com>
Date:	Mon,  4 May 2015 03:09:36 -0700
From:	Omar Sandoval <osandov@...ndov.com>
To:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org
Cc:	Omar Sandoval <osandov@...ndov.com>
Subject: [PATCH] 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
[wake up from 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.

Fixes: 3c18d447b3b3 ("sched/core: Check for available DL bandwidth in
cpuset_cpu_inactive()")

Signed-off-by: Omar Sandoval <osandov@...ndov.com>
---
This applies to v4.1-rc2.

I'm not familiar with this part of the kernel at all, but this Seems
Right (TM). If it isn't, consider this a bug report-plus.

Thanks!

 kernel/sched/core.c | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fe22f7510bce..ecf05bf39525 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6997,27 +6997,23 @@ 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:
-- 
2.3.7

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