Patch "workqueue: make sysfs of unbound kworker cpumask more clever" has been added to the 5.14-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    workqueue: make sysfs of unbound kworker cpumask more clever

to the 5.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     workqueue-make-sysfs-of-unbound-kworker-cpumask-more.patch
and it can be found in the queue-5.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 6a2057b00f62fea7f86f68ba482b9c6681ff0a0f
Author: Menglong Dong <imagedong@xxxxxxxxxxx>
Date:   Sun Oct 17 20:04:02 2021 +0800

    workqueue: make sysfs of unbound kworker cpumask more clever
    
    [ Upstream commit d25302e46592c97d29f70ccb1be558df31a9a360 ]
    
    Some unfriendly component, such as dpdk, write the same mask to
    unbound kworker cpumask again and again. Every time it write to
    this interface some work is queue to cpu, even though the mask
    is same with the original mask.
    
    So, fix it by return success and do nothing if the cpumask is
    equal with the old one.
    
    Signed-off-by: Mengen Sun <mengensun@xxxxxxxxxxx>
    Signed-off-by: Menglong Dong <imagedong@xxxxxxxxxxx>
    Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 542c2d03dab65..ccad28bf21e26 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5340,9 +5340,6 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 	int ret = -EINVAL;
 	cpumask_var_t saved_cpumask;
 
-	if (!zalloc_cpumask_var(&saved_cpumask, GFP_KERNEL))
-		return -ENOMEM;
-
 	/*
 	 * Not excluding isolated cpus on purpose.
 	 * If the user wishes to include them, we allow that.
@@ -5350,6 +5347,15 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 	cpumask_and(cpumask, cpumask, cpu_possible_mask);
 	if (!cpumask_empty(cpumask)) {
 		apply_wqattrs_lock();
+		if (cpumask_equal(cpumask, wq_unbound_cpumask)) {
+			ret = 0;
+			goto out_unlock;
+		}
+
+		if (!zalloc_cpumask_var(&saved_cpumask, GFP_KERNEL)) {
+			ret = -ENOMEM;
+			goto out_unlock;
+		}
 
 		/* save the old wq_unbound_cpumask. */
 		cpumask_copy(saved_cpumask, wq_unbound_cpumask);
@@ -5362,10 +5368,11 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 		if (ret < 0)
 			cpumask_copy(wq_unbound_cpumask, saved_cpumask);
 
+		free_cpumask_var(saved_cpumask);
+out_unlock:
 		apply_wqattrs_unlock();
 	}
 
-	free_cpumask_var(saved_cpumask);
 	return ret;
 }