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Subject[PATCH 4/5] kmod: Remove unecessary explicit wide CPU affinity setting
Date
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@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.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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