Re: [PATCH v16 00/13] support "task_isolation" mode

On Fri, Nov 03, 2017 at 01:04:39PM -0400, Chris Metcalf wrote:

Here, finally, is a new spin of the task isolation work (v16), with
changes based on the issues that were raised at last year's Linux
Plumbers Conference and in the email discussion that followed.

Hi Chris,

There's another possible way to break task isolation, by net subsystem.
See patch below.

Yury

From 8025e9330bf06ce146d4ba96833aad6eafe24759 Mon Sep 17 00:00:00 2001

From: Yury Norov <redacted>
Date: Sun, 8 Jul 2018 00:40:46 +0300
Subject: [PATCH] net: don't let user assign task isolation CPUs for RPS

Receive Packet Steering (RPS) subsystem distributes network traffic
handling to CPUs defined by user in
/sys/class/net/<dev>/queues/rx-<n>/rps_cpus.

If rps_cpus intersects with task_isolation_map, RPS may break task
isolation by assigning RPS work to CPU that runs isolated task.

In this patch user-provided rps_cpus map filtered to avoid that.

Signed-off-by: Yury Norov <redacted>
---
 include/linux/isolation.h |  2 ++
 net/core/net-sysfs.c      | 13 +++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/isolation.h b/include/linux/isolation.h
index f467545ad37d..b7f0a9085b13 100644
--- a/include/linux/isolation.h
+++ b/include/linux/isolation.h

@@ -14,6 +14,8 @@ struct task_struct;
 
 #ifdef CONFIG_TASK_ISOLATION
 
+extern cpumask_var_t task_isolation_map;
+
 /**
  * task_isolation_request() - prctl hook to request task isolation
  * @flags:	Flags from <linux/prctl.h> PR_TASK_ISOLATION_xxx.

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 927a6dcbad96..18e576893984 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c

@@ -11,6 +11,7 @@
 
 #include <linux/capability.h>
 #include <linux/kernel.h>
+#include <linux/isolation.h>
 #include <linux/netdevice.h>
 #include <net/switchdev.h>
 #include <linux/if_arp.h>

@@ -727,6 +728,18 @@ static ssize_t store_rps_map(struct netdev_rx_queue *queue,
 		return err;
 	}
 
+#ifdef CONFIG_TASK_ISOLATION
+	if (cpumask_intersects(mask, task_isolation_map)) {
+		char tmp[256];
+
+		pr_warn("RPS is not allowed on CPUs allocated for isolated tasks\n");
+
+		cpumask_andnot(mask, mask, task_isolation_map);
+		cpumap_print_to_pagebuf(1, tmp, mask);
+		pr_warn("RPS CPUs list is reduced to: %s\n", tmp);
+	}
+#endif
+
 	map = kzalloc(max_t(unsigned int,
 			    RPS_MAP_SIZE(cpumask_weight(mask)), L1_CACHE_BYTES),
 		      GFP_KERNEL);

-- 
2.17.1