1/*	$NetBSD: linux_kthread.c,v 1.9 2021/12/19 12:43:05 riastradh Exp $	*/
2
3/*-
4 * Copyright (c) 2021 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Taylor R. Campbell.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32#include <sys/cdefs.h>
33__KERNEL_RCSID(0, "$NetBSD: linux_kthread.c,v 1.9 2021/12/19 12:43:05 riastradh Exp $");
34
35#include <sys/types.h>
36
37#include <sys/condvar.h>
38#include <sys/kmem.h>
39#include <sys/kthread.h>
40#include <sys/lwp.h>
41#include <sys/mutex.h>
42#include <sys/specificdata.h>
43
44#include <linux/err.h>
45#include <linux/kthread.h>
46#include <linux/spinlock.h>
47
48#include <drm/drm_wait_netbsd.h>
49
50struct task_struct {
51	kmutex_t	kt_lock;
52	kcondvar_t	kt_cv;
53	bool		kt_shouldstop:1;
54	bool		kt_shouldpark:1;
55	bool		kt_parked:1;
56	bool		kt_exited:1;
57	int		kt_ret;
58
59	int		(*kt_func)(void *);
60	void		*kt_cookie;
61	spinlock_t	*kt_interlock;
62	drm_waitqueue_t	*kt_wq;
63	struct lwp	*kt_lwp;
64};
65
66static specificdata_key_t linux_kthread_key __read_mostly = -1;
67
68int
69linux_kthread_init(void)
70{
71	int error;
72
73	error = lwp_specific_key_create(&linux_kthread_key, NULL);
74	if (error)
75		goto out;
76
77	/* Success!  */
78	error = 0;
79
80out:	if (error)
81		linux_kthread_fini();
82	return error;
83}
84
85void
86linux_kthread_fini(void)
87{
88
89	if (linux_kthread_key != -1) {
90		lwp_specific_key_delete(linux_kthread_key);
91		linux_kthread_key = -1;
92	}
93}
94
95#define	linux_kthread()	_linux_kthread(__func__)
96static struct task_struct *
97_linux_kthread(const char *caller)
98{
99	struct task_struct *T;
100
101	T = lwp_getspecific(linux_kthread_key);
102	KASSERTMSG(T != NULL, "%s must be called from Linux kthread", caller);
103
104	return T;
105}
106
107static void
108linux_kthread_start(void *cookie)
109{
110	struct task_struct *T = cookie;
111	int ret;
112
113	lwp_setspecific(linux_kthread_key, T);
114
115	ret = (*T->kt_func)(T->kt_cookie);
116
117	/*
118	 * Mark the thread exited, set the return value, and wake any
119	 * waiting kthread_stop.
120	 */
121	mutex_enter(&T->kt_lock);
122	T->kt_exited = true;
123	T->kt_ret = ret;
124	cv_broadcast(&T->kt_cv);
125	mutex_exit(&T->kt_lock);
126
127	/* Exit the (NetBSD) kthread.  */
128	kthread_exit(0);
129}
130
131static struct task_struct *
132kthread_alloc(int (*func)(void *), void *cookie, spinlock_t *interlock,
133    drm_waitqueue_t *wq)
134{
135	struct task_struct *T;
136
137	T = kmem_zalloc(sizeof(*T), KM_SLEEP);
138
139	mutex_init(&T->kt_lock, MUTEX_DEFAULT, IPL_VM);
140	cv_init(&T->kt_cv, "lnxkthrd");
141
142	T->kt_shouldstop = false;
143	T->kt_shouldpark = false;
144	T->kt_parked = false;
145	T->kt_exited = false;
146	T->kt_ret = 0;
147
148	T->kt_func = func;
149	T->kt_cookie = cookie;
150	T->kt_interlock = interlock;
151	T->kt_wq = wq;
152
153	return T;
154}
155
156static void
157kthread_free(struct task_struct *T)
158{
159
160	KASSERT(T->kt_exited);
161
162	cv_destroy(&T->kt_cv);
163	mutex_destroy(&T->kt_lock);
164	kmem_free(T, sizeof(*T));
165}
166
167struct task_struct *
168kthread_run(int (*func)(void *), void *cookie, const char *name,
169    spinlock_t *interlock, drm_waitqueue_t *wq)
170{
171	struct task_struct *T;
172	int error;
173
174	T = kthread_alloc(func, cookie, interlock, wq);
175	error = kthread_create(PRI_NONE, KTHREAD_MPSAFE, NULL,
176	    linux_kthread_start, T, &T->kt_lwp, "%s", name);
177	if (error) {
178		kthread_free(T);
179		return ERR_PTR(-error); /* XXX errno NetBSD->Linux */
180	}
181
182	return T;
183}
184
185int
186kthread_stop(struct task_struct *T)
187{
188	int ret;
189
190	/* Lock order: interlock, then kthread lock.  */
191	spin_lock(T->kt_interlock);
192	mutex_enter(&T->kt_lock);
193
194	/*
195	 * Notify the thread that it's stopping, and wake it if it's
196	 * parked or sleeping on its own waitqueue.
197	 */
198	T->kt_shouldpark = false;
199	T->kt_shouldstop = true;
200	cv_broadcast(&T->kt_cv);
201	DRM_SPIN_WAKEUP_ALL(T->kt_wq, T->kt_interlock);
202
203	/* Release the interlock while we wait for thread to finish.  */
204	spin_unlock(T->kt_interlock);
205
206	/* Wait for the thread to finish.  */
207	while (!T->kt_exited)
208		cv_wait(&T->kt_cv, &T->kt_lock);
209
210	/* Grab the return code and release the lock -- we're done.  */
211	ret = T->kt_ret;
212	mutex_exit(&T->kt_lock);
213
214	/* Free the (Linux) kthread.  */
215	kthread_free(T);
216
217	/* Return what the thread returned.  */
218	return ret;
219}
220
221int
222kthread_should_stop(void)
223{
224	struct task_struct *T = linux_kthread();
225	bool shouldstop;
226
227	mutex_enter(&T->kt_lock);
228	shouldstop = T->kt_shouldstop;
229	mutex_exit(&T->kt_lock);
230
231	return shouldstop;
232}
233
234void
235kthread_park(struct task_struct *T)
236{
237
238	/* Lock order: interlock, then kthread lock.  */
239	spin_lock(T->kt_interlock);
240	mutex_enter(&T->kt_lock);
241
242	/* Caller must not ask to park if they've already asked to stop.  */
243	KASSERT(!T->kt_shouldstop);
244
245	/* Ask the thread to park.  */
246	T->kt_shouldpark = true;
247
248	/*
249	 * Ensure the thread is not sleeping on its condvar.  After
250	 * this point, we are done with the interlock, which we must
251	 * not hold while we wait on the kthread condvar.
252	 */
253	DRM_SPIN_WAKEUP_ALL(T->kt_wq, T->kt_interlock);
254	spin_unlock(T->kt_interlock);
255
256	/*
257	 * Wait until the thread has issued kthread_parkme, unless we
258	 * are already the thread, which Linux allows and interprets to
259	 * mean don't wait.
260	 */
261	if (T->kt_lwp != curlwp) {
262		while (!T->kt_parked)
263			cv_wait(&T->kt_cv, &T->kt_lock);
264	}
265
266	/* Release the kthread lock too.  */
267	mutex_exit(&T->kt_lock);
268}
269
270void
271kthread_unpark(struct task_struct *T)
272{
273
274	mutex_enter(&T->kt_lock);
275	T->kt_shouldpark = false;
276	cv_broadcast(&T->kt_cv);
277	mutex_exit(&T->kt_lock);
278}
279
280int
281__kthread_should_park(struct task_struct *T)
282{
283	bool shouldpark;
284
285	mutex_enter(&T->kt_lock);
286	shouldpark = T->kt_shouldpark;
287	mutex_exit(&T->kt_lock);
288
289	return shouldpark;
290}
291
292int
293kthread_should_park(void)
294{
295	struct task_struct *T = linux_kthread();
296
297	return __kthread_should_park(T);
298}
299
300void
301kthread_parkme(void)
302{
303	struct task_struct *T = linux_kthread();
304
305	assert_spin_locked(T->kt_interlock);
306
307	spin_unlock(T->kt_interlock);
308	mutex_enter(&T->kt_lock);
309	while (T->kt_shouldpark) {
310		T->kt_parked = true;
311		cv_broadcast(&T->kt_cv);
312		cv_wait(&T->kt_cv, &T->kt_lock);
313		T->kt_parked = false;
314	}
315	mutex_exit(&T->kt_lock);
316	spin_lock(T->kt_interlock);
317}
318