linux-kernel - [PATCH 4/5] kmod: Remove unecessary explicit wide CPU affinity setting

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Date:	Thu,  9 Jul 2015 20:07:16 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 4/5] kmod: Remove unecessary explicit wide CPU affinity setting

The call_usermodehelper_exec_[a]sync() kernel threads are created by
unbound workqueues precisely because we want them to be affine to all
CPUs, irrespective of any call_usermodehelper() caller with possibly
reduced CPU affinity. So this explicit all-CPUs wide affinity forcing is
useless.

Not only useless it even adds disturbance on isolated CPUs in nohz full
configurations where users set the unbound workqueues low level cpumask
to a reduced set in order to execute non-user-critical work on
housekeeping dedicated CPUs. This reduced affinity is naturally
inherited to usermodehelper kernel threads but the explicit call to
set_cpus_allowed_ptr() breaks that.

So just remove it.

Cc: Rik van Riel <riel@...hat.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Christoph Lameter <cl@...ux.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
 kernel/kmod.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 9ffb24c..d190178 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -221,9 +221,6 @@ static int call_usermodehelper_exec_async(void *data)
 	flush_signal_handlers(current, 1);
 	spin_unlock_irq(&current->sighand->siglock);

-	/* We can run anywhere, unlike our parent (unbound workqueue). */
-	set_cpus_allowed_ptr(current, cpu_all_mask);
-
 	/*
 	 * Our parent is the unbound workqueue, which runs with elevated
 	 * scheduling priority. Avoid propagating that into the userspace child.
-- 
2.1.4

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