linux-kernel - [PATCH 1/1] usermodehelper: kill ____call_usermodehelper()->set_cpus_allowed

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Message-ID: <20131128193349.GB24767@redhat.com>
Date:	Thu, 28 Nov 2013 20:33:49 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Tejun Heo <htejun@...il.com>, zhang.yi20@....com.cn,
	lkml <linux-kernel@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Ingo Molnar <mingo@...hat.com>
Subject: [PATCH 1/1] usermodehelper: kill
	____call_usermodehelper()->set_cpus_allowed_ptr()

____call_usermodehelper() does set_cpus_allowed_ptr(cpu_all_mask),
this (and the comment) is misleading. We no longer have keventd_wq,
and kmod.c switched to khelper_wq a long ago.

And more importantly, "unlike our parent" is no longer true too,
this thread was created by WQ_UNBOUND worker thread which has the
full ->cpus_allowed mask, so this set_cpus_allowed_ptr() is simply
unnecessary.

Perhaps we will change this later, so that userspace can control
the affinity of the usermode helper tasks, but this is yet another
reason to remove this set_cpus_allowed_ptr().

To some degree this also applies to set_user_nice(), but this
patch only updates the comment.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/kmod.c |    8 ++------
 1 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/kernel/kmod.c b/kernel/kmod.c
index b086006..2fe4544 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -208,13 +208,9 @@ static int ____call_usermodehelper(void *data)
 	spin_lock_irq(&current->sighand->siglock);
 	flush_signal_handlers(current, 1);
 	spin_unlock_irq(&current->sighand->siglock);
-
-	/* We can run anywhere, unlike our parent keventd(). */
-	set_cpus_allowed_ptr(current, cpu_all_mask);
-
 	/*
-	 * Our parent is keventd, which runs with elevated scheduling priority.
-	 * Avoid propagating that into the userspace child.
+	 * Our parent is a workqueue thread, which can run with elevated
+	 * scheduling priority. Avoid propagating that into the userspace.
 	 */
 	set_user_nice(current, 0);
 
-- 
1.5.5.1


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