linux-kernel - [PATCH] Revert "isolcpus: Affine unbound kernel threads to housekeeping cpus"

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 7 May 2021 13:57:10 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Phil Auld <pauld@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] Revert "isolcpus: Affine unbound kernel threads to
 housekeeping cpus"



commit 9cc5b8656892a72438ee7deb introduced a new housekeeping flag,
HK_FLAG_KTHREAD, that when enabled sets the CPU affinity for the 
kthreadd process (therefore all unbounded kernel threads created
from that point on will use the housekeeping cpumask).

This is not necessary, since its possible to control placement of
kthreadd from userspace:

# taskset -c -p 0 `pgrep kthreadd`
pid 2's current affinity list: 1
pid 2's new affinity list: 0

Unbounded kernel threads started from that point on will inherit
the kthreadd cpumask.

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>

Index: linux-2.6/include/linux/sched/isolation.h
===================================================================
--- linux-2.6.orig/include/linux/sched/isolation.h
+++ linux-2.6/include/linux/sched/isolation.h
@@ -14,7 +14,6 @@ enum hk_flags {
 	HK_FLAG_DOMAIN		= (1 << 5),
 	HK_FLAG_WQ		= (1 << 6),
 	HK_FLAG_MANAGED_IRQ	= (1 << 7),
-	HK_FLAG_KTHREAD		= (1 << 8),
 };
 
 #ifdef CONFIG_CPU_ISOLATION
Index: linux-2.6/kernel/kthread.c
===================================================================
--- linux-2.6.orig/kernel/kthread.c
+++ linux-2.6/kernel/kthread.c
@@ -27,7 +27,6 @@
 #include <linux/ptrace.h>
 #include <linux/uaccess.h>
 #include <linux/numa.h>
-#include <linux/sched/isolation.h>
 #include <trace/events/sched.h>
 
 
@@ -405,8 +404,7 @@ struct task_struct *__kthread_create_on_
 		 * The kernel thread should not inherit these properties.
 		 */
 		sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
-		set_cpus_allowed_ptr(task,
-				     housekeeping_cpumask(HK_FLAG_KTHREAD));
+		set_cpus_allowed_ptr(task, cpu_possible_mask);
 	}
 	kfree(create);
 	return task;
@@ -655,7 +653,7 @@ int kthreadd(void *unused)
 	/* Setup a clean context for our children to inherit. */
 	set_task_comm(tsk, "kthreadd");
 	ignore_signals(tsk);
-	set_cpus_allowed_ptr(tsk, housekeeping_cpumask(HK_FLAG_KTHREAD));
+	set_cpus_allowed_ptr(tsk, cpu_possible_mask);
 	set_mems_allowed(node_states[N_MEMORY]);
 
 	current->flags |= PF_NOFREEZE;
Index: linux-2.6/kernel/sched/isolation.c
===================================================================
--- linux-2.6.orig/kernel/sched/isolation.c
+++ linux-2.6/kernel/sched/isolation.c
@@ -140,8 +140,7 @@ static int __init housekeeping_nohz_full
 {
 	unsigned int flags;
 
-	flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU |
-		HK_FLAG_MISC | HK_FLAG_KTHREAD;
+	flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU | HK_FLAG_MISC;
 
 	return housekeeping_setup(str, flags);
 }