workqueue: Add workqueue_unbound_exclude_cpumask() to exclude CPUs from wq_unbound_cpumask

JIRA: https://issues.redhat.com/browse/RHEL-21798
Conflicts:
 1) A merge conflict in the workqueue_unbound_exclude_cpumask() hunk
    of kernel/workqueue.c due to missing upstream commit 63c5484
    ("workqueue: Add multiple affinity scopes and interface to select
    them").
 2) A merge conflict in the workqueue_init_early() hunk of
    kernel/workqueue.c due to upstream merge conflict resolved according
    to upstream merge commit 2025956 ("Merge branch 'for-6.7-fixes'
    of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq into for-6.8").

commit fe28f63
Author: Waiman Long <[email protected]>
Date:   Wed, 25 Oct 2023 14:25:52 -0400

    workqueue: Add workqueue_unbound_exclude_cpumask() to exclude CPUs from wq_unbound_cpumask

    When the "isolcpus" boot command line option is used to add a set
    of isolated CPUs, those CPUs will be excluded automatically from
    wq_unbound_cpumask to avoid running work functions from unbound
    workqueues.

    Recently cpuset has been extended to allow the creation of partitions
    of isolated CPUs dynamically. To make it closer to the "isolcpus"
    in functionality, the CPUs in those isolated cpuset partitions should be
    excluded from wq_unbound_cpumask as well. This can be done currently by
    explicitly writing to the workqueue's cpumask sysfs file after creating
    the isolated partitions. However, this process can be error prone.

    Ideally, the cpuset code should be allowed to request the workqueue code
    to exclude those isolated CPUs from wq_unbound_cpumask so that this
    operation can be done automatically and the isolated CPUs will be returned
    back to wq_unbound_cpumask after the destructions of the isolated
    cpuset partitions.

    This patch adds a new workqueue_unbound_exclude_cpumask() function to
    enable that. This new function will exclude the specified isolated
    CPUs from wq_unbound_cpumask. To be able to restore those isolated
    CPUs back after the destruction of isolated cpuset partitions, a new
    wq_requested_unbound_cpumask is added to store the user provided unbound
    cpumask either from the boot command line options or from writing to
    the cpumask sysfs file. This new cpumask provides the basis for CPU
    exclusion.

    To enable users to understand how the wq_unbound_cpumask is being
    modified internally, this patch also exposes the newly introduced
    wq_requested_unbound_cpumask as well as a wq_isolated_cpumask to
    store the cpumask to be excluded from wq_unbound_cpumask as read-only
    sysfs files.

    Signed-off-by: Waiman Long <[email protected]>
    Signed-off-by: Tejun Heo <[email protected]>

Signed-off-by: Waiman Long <[email protected]>

Author: Waiman-Long

include/linux/workqueue.h

@@ -434,7 +434,7 @@ struct workqueue_attrs *alloc_workqueue_attrs(void);
 void free_workqueue_attrs(struct workqueue_attrs *attrs);
 int apply_workqueue_attrs(struct workqueue_struct *wq,
 			  const struct workqueue_attrs *attrs);
-int workqueue_set_unbound_cpumask(cpumask_var_t cpumask);
+extern int workqueue_unbound_exclude_cpumask(cpumask_var_t cpumask);
 
 extern bool queue_work_on(int cpu, struct workqueue_struct *wq,
 			struct work_struct *work);

kernel/workqueue.c

@@ -327,6 +327,12 @@ static bool workqueue_freezing;		/* PL: have wqs started freezing? */
 /* PL&A: allowable cpus for unbound wqs and work items */
 static cpumask_var_t wq_unbound_cpumask;
 
+/* PL: user requested unbound cpumask via sysfs */
+static cpumask_var_t wq_requested_unbound_cpumask;
+
+/* PL: isolated cpumask to be excluded from unbound cpumask */
+static cpumask_var_t wq_isolated_cpumask;
+
 /* for further constrain wq_unbound_cpumask by cmdline parameter*/
 static struct cpumask wq_cmdline_cpumask __initdata;
 
@@ -5494,7 +5500,7 @@ static int workqueue_apply_unbound_cpumask(const cpumask_var_t unbound_cpumask)
  *  		-EINVAL	- Invalid @cpumask
  *  		-ENOMEM	- Failed to allocate memory for attrs or pwqs.
  */
-int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
+static int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 {
 	int ret = -EINVAL;
 
@@ -5505,6 +5511,7 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 	cpumask_and(cpumask, cpumask, cpu_possible_mask);
 	if (!cpumask_empty(cpumask)) {
 		apply_wqattrs_lock();
+		cpumask_copy(wq_requested_unbound_cpumask, cpumask);
 		if (cpumask_equal(cpumask, wq_unbound_cpumask)) {
 			ret = 0;
 			goto out_unlock;
@@ -5519,6 +5526,44 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 	return ret;
 }
 
+/**
+ * workqueue_unbound_exclude_cpumask - Exclude given CPUs from unbound cpumask
+ * @exclude_cpumask: the cpumask to be excluded from wq_unbound_cpumask
+ *
+ * This function can be called from cpuset code to provide a set of isolated
+ * CPUs that should be excluded from wq_unbound_cpumask. The caller must hold
+ * either cpus_read_lock or cpus_write_lock.
+ */
+int workqueue_unbound_exclude_cpumask(cpumask_var_t exclude_cpumask)
+{
+	cpumask_var_t cpumask;
+	int ret = 0;
+
+	if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
+		return -ENOMEM;
+
+	lockdep_assert_cpus_held();
+	mutex_lock(&wq_pool_mutex);
+
+	/* Save the current isolated cpumask & export it via sysfs */
+	cpumask_copy(wq_isolated_cpumask, exclude_cpumask);
+
+	/*
+	 * If the operation fails, it will fall back to
+	 * wq_requested_unbound_cpumask which is initially set to
+	 * (HK_TYPE_WQ ∩ HK_TYPE_DOMAIN) house keeping mask and rewritten
+	 * by any subsequent write to workqueue/cpumask sysfs file.
+	 */
+	if (!cpumask_andnot(cpumask, wq_requested_unbound_cpumask, exclude_cpumask))
+		cpumask_copy(cpumask, wq_requested_unbound_cpumask);
+	if (!cpumask_equal(cpumask, wq_unbound_cpumask))
+		ret = workqueue_apply_unbound_cpumask(cpumask);
+
+	mutex_unlock(&wq_pool_mutex);
+	free_cpumask_var(cpumask);
+	return ret;
+}
+
 #ifdef CONFIG_SYSFS
 /*
  * Workqueues with WQ_SYSFS flag set is visible to userland via
@@ -5750,19 +5795,36 @@ static struct bus_type wq_subsys = {
 	.dev_groups			= wq_sysfs_groups,
 };
 
-static ssize_t wq_unbound_cpumask_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
+static ssize_t __wq_cpumask_show(struct device *dev,
+		struct device_attribute *attr, char *buf, cpumask_var_t mask)
 {
 	int written;
 
 	mutex_lock(&wq_pool_mutex);
-	written = scnprintf(buf, PAGE_SIZE, "%*pb\n",
-			    cpumask_pr_args(wq_unbound_cpumask));
+	written = scnprintf(buf, PAGE_SIZE, "%*pb\n", cpumask_pr_args(mask));
 	mutex_unlock(&wq_pool_mutex);
 
 	return written;
 }
 
+static ssize_t wq_unbound_cpumask_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	return __wq_cpumask_show(dev, attr, buf, wq_unbound_cpumask);
+}
+
+static ssize_t wq_requested_cpumask_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	return __wq_cpumask_show(dev, attr, buf, wq_requested_unbound_cpumask);
+}
+
+static ssize_t wq_isolated_cpumask_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	return __wq_cpumask_show(dev, attr, buf, wq_isolated_cpumask);
+}
+
 static ssize_t wq_unbound_cpumask_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t count)
 {
@@ -5780,9 +5842,13 @@ static ssize_t wq_unbound_cpumask_store(struct device *dev,
 	return ret ? ret : count;
 }
 
-static struct device_attribute wq_sysfs_cpumask_attr =
+static struct device_attribute wq_sysfs_cpumask_attrs[] = {
 	__ATTR(cpumask, 0644, wq_unbound_cpumask_show,
-	       wq_unbound_cpumask_store);
+	       wq_unbound_cpumask_store),
+	__ATTR(cpumask_requested, 0444, wq_requested_cpumask_show, NULL),
+	__ATTR(cpumask_isolated, 0444, wq_isolated_cpumask_show, NULL),
+	__ATTR_NULL,
+};
 
 static int __init wq_sysfs_init(void)
 {
@@ -5795,7 +5861,13 @@ static int __init wq_sysfs_init(void)
 
 	dev_root = bus_get_dev_root(&wq_subsys);
 	if (dev_root) {
-		err = device_create_file(dev_root, &wq_sysfs_cpumask_attr);
+		struct device_attribute *attr;
+
+		for (attr = wq_sysfs_cpumask_attrs; attr->attr.name; attr++) {
+			err = device_create_file(dev_root, attr);
+			if (err)
+				break;
+		}
 		put_device(dev_root);
 	}
 	return err;
@@ -6118,11 +6190,14 @@ void __init workqueue_init_early(void)
 	BUILD_BUG_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));
 
 	BUG_ON(!alloc_cpumask_var(&wq_unbound_cpumask, GFP_KERNEL));
+	BUG_ON(!alloc_cpumask_var(&wq_requested_unbound_cpumask, GFP_KERNEL));
+	BUG_ON(!zalloc_cpumask_var(&wq_isolated_cpumask, GFP_KERNEL));
 	cpumask_copy(wq_unbound_cpumask, cpu_possible_mask);
 	restrict_unbound_cpumask("HK_TYPE_WQ", housekeeping_cpumask(HK_TYPE_WQ));
 	restrict_unbound_cpumask("HK_TYPE_DOMAIN", housekeeping_cpumask(HK_TYPE_DOMAIN));
 	if (!cpumask_empty(&wq_cmdline_cpumask))
 		restrict_unbound_cpumask("workqueue.unbound_cpus", &wq_cmdline_cpumask);
+	cpumask_copy(wq_requested_unbound_cpumask, wq_unbound_cpumask);
 
 	pwq_cache = KMEM_CACHE(pool_workqueue, SLAB_PANIC);