[PATCH] workqueue.c: Change workqueue to accept variable length name

[Audra Mitchell <audra@redhat.com>]

Currently we limit the size of the workqueue name to 24 characters due to
commit ecf6881ff349 ("workqueue: make workqueue->name[] fixed len")
As device names increase in size a static size for the workqueue name no
longer satisfies the size requirement, leading to truncated workqueue
names as we append the device name to the workqueue name. Truncation of
the workqueue names can cause issues when debugging as each is unique to
the associated device. Bring back the flexibility of a variable length
workqueue name to prevent truncation.

Signed-off-by: Audra Mitchell <audra@redhat.com>
---
 kernel/workqueue.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 2989b57e154a..6e9e332d1cf4 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -107,8 +107,6 @@ enum {
 	 */
 	RESCUER_NICE_LEVEL	= MIN_NICE,
 	HIGHPRI_NICE_LEVEL	= MIN_NICE,
-
-	WQ_NAME_LEN		= 24,
 };
 
 /*
@@ -311,7 +309,7 @@ struct workqueue_struct {
 	struct lock_class_key	key;
 	struct lockdep_map	lockdep_map;
 #endif
-	char			name[WQ_NAME_LEN]; /* I: workqueue name */
+	char			*name; /* I: workqueue name */
 
 	/*
 	 * Destruction of workqueue_struct is RCU protected to allow walking
@@ -3929,6 +3927,7 @@ static void rcu_free_wq(struct rcu_head *rcu)
 	wq_free_lockdep(wq);
 	free_percpu(wq->cpu_pwq);
 	free_workqueue_attrs(wq->unbound_attrs);
+	kfree(wq->name);
 	kfree(wq);
 }
 
@@ -4670,9 +4669,10 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 					 unsigned int flags,
 					 int max_active, ...)
 {
-	va_list args;
+	va_list args, args_copy;
 	struct workqueue_struct *wq;
 	struct pool_workqueue *pwq;
+	size_t namelen;
 
 	/*
 	 * Unbound && max_active == 1 used to imply ordered, which is no longer
@@ -4699,8 +4699,16 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 	}
 
 	va_start(args, max_active);
-	vsnprintf(wq->name, sizeof(wq->name), fmt, args);
+	va_copy(args_copy, args);
+	namelen = vsnprintf(NULL, 0, fmt, args) + 1;
+	namelen = (namelen < PAGE_SIZE) ? namelen : PAGE_SIZE;
 	va_end(args);
+	wq->name = kzalloc(namelen, GFP_KERNEL);
+	if (!wq->name)
+		goto err_free_wq;
+
+	vsnprintf(wq->name, namelen, fmt, args_copy);
+	va_end(args_copy);
 
 	max_active = max_active ?: WQ_DFL_ACTIVE;
 	max_active = wq_clamp_max_active(max_active, flags, wq->name);
@@ -4746,6 +4754,7 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 	return wq;
 
 err_unreg_lockdep:
+	kfree(wq->name);
 	wq_unregister_lockdep(wq);
 	wq_free_lockdep(wq);
 err_free_wq:
@@ -5038,7 +5047,7 @@ EXPORT_SYMBOL_GPL(set_worker_desc);
 void print_worker_info(const char *log_lvl, struct task_struct *task)
 {
 	work_func_t *fn = NULL;
-	char name[WQ_NAME_LEN] = { };
+	char *name;
 	char desc[WORKER_DESC_LEN] = { };
 	struct pool_workqueue *pwq = NULL;
 	struct workqueue_struct *wq = NULL;
@@ -5060,7 +5069,7 @@ void print_worker_info(const char *log_lvl, struct task_struct *task)
 	copy_from_kernel_nofault(&fn, &worker->current_func, sizeof(fn));
 	copy_from_kernel_nofault(&pwq, &worker->current_pwq, sizeof(pwq));
 	copy_from_kernel_nofault(&wq, &pwq->wq, sizeof(wq));
-	copy_from_kernel_nofault(name, wq->name, sizeof(name) - 1);
+	copy_from_kernel_nofault(&name, &wq->name, sizeof(wq->name));
 	copy_from_kernel_nofault(desc, worker->desc, sizeof(desc) - 1);
 
 	if (fn || name[0] || desc[0]) {
-- 
2.43.0