rtld_lock.c revision 312701 
1/*-
2 * Copyright 1999, 2000 John D. Polstra.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 *
25 *	from: FreeBSD: src/libexec/rtld-elf/sparc64/lockdflt.c,v 1.3 2002/10/09
26 * $FreeBSD: stable/10/libexec/rtld-elf/rtld_lock.c 312701 2017-01-24 17:30:13Z kib $
27 */
28
29/*
30 * Thread locking implementation for the dynamic linker.
31 *
32 * We use the "simple, non-scalable reader-preference lock" from:
33 *
34 *   J. M. Mellor-Crummey and M. L. Scott. "Scalable Reader-Writer
35 *   Synchronization for Shared-Memory Multiprocessors." 3rd ACM Symp. on
36 *   Principles and Practice of Parallel Programming, April 1991.
37 *
38 * In this algorithm the lock is a single word.  Its low-order bit is
39 * set when a writer holds the lock.  The remaining high-order bits
40 * contain a count of readers desiring the lock.  The algorithm requires
41 * atomic "compare_and_store" and "add" operations, which we take
42 * from machine/atomic.h.
43 */
44
45#include <sys/param.h>
46#include <signal.h>
47#include <stdlib.h>
48#include <time.h>
49
50#include "debug.h"
51#include "rtld.h"
52#include "rtld_machdep.h"
53
54void _rtld_thread_init(struct RtldLockInfo *) __exported;
55void _rtld_atfork_pre(int *) __exported;
56void _rtld_atfork_post(int *) __exported;
57
58#define WAFLAG		0x1	/* A writer holds the lock */
59#define RC_INCR		0x2	/* Adjusts count of readers desiring lock */
60
61typedef struct Struct_Lock {
62	volatile u_int lock;
63	void *base;
64} Lock;
65
66static sigset_t fullsigmask, oldsigmask;
67static int thread_flag, wnested;
68
69static void *
70def_lock_create(void)
71{
72    void *base;
73    char *p;
74    uintptr_t r;
75    Lock *l;
76
77    /*
78     * Arrange for the lock to occupy its own cache line.  First, we
79     * optimistically allocate just a cache line, hoping that malloc
80     * will give us a well-aligned block of memory.  If that doesn't
81     * work, we allocate a larger block and take a well-aligned cache
82     * line from it.
83     */
84    base = xmalloc(CACHE_LINE_SIZE);
85    p = (char *)base;
86    if ((uintptr_t)p % CACHE_LINE_SIZE != 0) {
87	free(base);
88	base = xmalloc(2 * CACHE_LINE_SIZE);
89	p = (char *)base;
90	if ((r = (uintptr_t)p % CACHE_LINE_SIZE) != 0)
91	    p += CACHE_LINE_SIZE - r;
92    }
93    l = (Lock *)p;
94    l->base = base;
95    l->lock = 0;
96    return l;
97}
98
99static void
100def_lock_destroy(void *lock)
101{
102    Lock *l = (Lock *)lock;
103
104    free(l->base);
105}
106
107static void
108def_rlock_acquire(void *lock)
109{
110    Lock *l = (Lock *)lock;
111
112    atomic_add_acq_int(&l->lock, RC_INCR);
113    while (l->lock & WAFLAG)
114	    ;	/* Spin */
115}
116
117static void
118def_wlock_acquire(void *lock)
119{
120	Lock *l;
121	sigset_t tmp_oldsigmask;
122
123	l = (Lock *)lock;
124	for (;;) {
125		sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask);
126		if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG))
127			break;
128		sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
129	}
130	if (atomic_fetchadd_int(&wnested, 1) == 0)
131		oldsigmask = tmp_oldsigmask;
132}
133
134static void
135def_lock_release(void *lock)
136{
137	Lock *l;
138
139	l = (Lock *)lock;
140	if ((l->lock & WAFLAG) == 0)
141		atomic_add_rel_int(&l->lock, -RC_INCR);
142	else {
143		assert(wnested > 0);
144		atomic_add_rel_int(&l->lock, -WAFLAG);
145		if (atomic_fetchadd_int(&wnested, -1) == 1)
146			sigprocmask(SIG_SETMASK, &oldsigmask, NULL);
147	}
148}
149
150static int
151def_thread_set_flag(int mask)
152{
153	int old_val = thread_flag;
154	thread_flag |= mask;
155	return (old_val);
156}
157
158static int
159def_thread_clr_flag(int mask)
160{
161	int old_val = thread_flag;
162	thread_flag &= ~mask;
163	return (old_val);
164}
165
166/*
167 * Public interface exposed to the rest of the dynamic linker.
168 */
169static struct RtldLockInfo lockinfo;
170static struct RtldLockInfo deflockinfo;
171
172static __inline int
173thread_mask_set(int mask)
174{
175	return lockinfo.thread_set_flag(mask);
176}
177
178static __inline void
179thread_mask_clear(int mask)
180{
181	lockinfo.thread_clr_flag(mask);
182}
183
184#define	RTLD_LOCK_CNT	3
185struct rtld_lock {
186	void	*handle;
187	int	 mask;
188} rtld_locks[RTLD_LOCK_CNT];
189
190rtld_lock_t	rtld_bind_lock = &rtld_locks[0];
191rtld_lock_t	rtld_libc_lock = &rtld_locks[1];
192rtld_lock_t	rtld_phdr_lock = &rtld_locks[2];
193
194void
195rlock_acquire(rtld_lock_t lock, RtldLockState *lockstate)
196{
197
198	if (lockstate == NULL)
199		return;
200
201	if (thread_mask_set(lock->mask) & lock->mask) {
202		dbg("rlock_acquire: recursed");
203		lockstate->lockstate = RTLD_LOCK_UNLOCKED;
204		return;
205	}
206	lockinfo.rlock_acquire(lock->handle);
207	lockstate->lockstate = RTLD_LOCK_RLOCKED;
208}
209
210void
211wlock_acquire(rtld_lock_t lock, RtldLockState *lockstate)
212{
213
214	if (lockstate == NULL)
215		return;
216
217	if (thread_mask_set(lock->mask) & lock->mask) {
218		dbg("wlock_acquire: recursed");
219		lockstate->lockstate = RTLD_LOCK_UNLOCKED;
220		return;
221	}
222	lockinfo.wlock_acquire(lock->handle);
223	lockstate->lockstate = RTLD_LOCK_WLOCKED;
224}
225
226void
227lock_release(rtld_lock_t lock, RtldLockState *lockstate)
228{
229
230	if (lockstate == NULL)
231		return;
232
233	switch (lockstate->lockstate) {
234	case RTLD_LOCK_UNLOCKED:
235		break;
236	case RTLD_LOCK_RLOCKED:
237	case RTLD_LOCK_WLOCKED:
238		thread_mask_clear(lock->mask);
239		lockinfo.lock_release(lock->handle);
240		break;
241	default:
242		assert(0);
243	}
244}
245
246void
247lock_upgrade(rtld_lock_t lock, RtldLockState *lockstate)
248{
249
250	if (lockstate == NULL)
251		return;
252
253	lock_release(lock, lockstate);
254	wlock_acquire(lock, lockstate);
255}
256
257void
258lock_restart_for_upgrade(RtldLockState *lockstate)
259{
260
261	if (lockstate == NULL)
262		return;
263
264	switch (lockstate->lockstate) {
265	case RTLD_LOCK_UNLOCKED:
266	case RTLD_LOCK_WLOCKED:
267		break;
268	case RTLD_LOCK_RLOCKED:
269		siglongjmp(lockstate->env, 1);
270		break;
271	default:
272		assert(0);
273	}
274}
275
276void
277lockdflt_init(void)
278{
279    int i;
280
281    deflockinfo.rtli_version  = RTLI_VERSION;
282    deflockinfo.lock_create   = def_lock_create;
283    deflockinfo.lock_destroy  = def_lock_destroy;
284    deflockinfo.rlock_acquire = def_rlock_acquire;
285    deflockinfo.wlock_acquire = def_wlock_acquire;
286    deflockinfo.lock_release  = def_lock_release;
287    deflockinfo.thread_set_flag = def_thread_set_flag;
288    deflockinfo.thread_clr_flag = def_thread_clr_flag;
289    deflockinfo.at_fork = NULL;
290
291    for (i = 0; i < RTLD_LOCK_CNT; i++) {
292	    rtld_locks[i].mask   = (1 << i);
293	    rtld_locks[i].handle = NULL;
294    }
295
296    memcpy(&lockinfo, &deflockinfo, sizeof(lockinfo));
297    _rtld_thread_init(NULL);
298    /*
299     * Construct a mask to block all signals except traps which might
300     * conceivably be generated within the dynamic linker itself.
301     */
302    sigfillset(&fullsigmask);
303    sigdelset(&fullsigmask, SIGILL);
304    sigdelset(&fullsigmask, SIGTRAP);
305    sigdelset(&fullsigmask, SIGABRT);
306    sigdelset(&fullsigmask, SIGEMT);
307    sigdelset(&fullsigmask, SIGFPE);
308    sigdelset(&fullsigmask, SIGBUS);
309    sigdelset(&fullsigmask, SIGSEGV);
310    sigdelset(&fullsigmask, SIGSYS);
311}
312
313/*
314 * Callback function to allow threads implementation to
315 * register their own locking primitives if the default
316 * one is not suitable.
317 * The current context should be the only context
318 * executing at the invocation time.
319 */
320void
321_rtld_thread_init(struct RtldLockInfo *pli)
322{
323	int flags, i;
324	void *locks[RTLD_LOCK_CNT];
325
326	/* disable all locking while this function is running */
327	flags =	thread_mask_set(~0);
328
329	if (pli == NULL)
330		pli = &deflockinfo;
331
332
333	for (i = 0; i < RTLD_LOCK_CNT; i++)
334		if ((locks[i] = pli->lock_create()) == NULL)
335			break;
336
337	if (i < RTLD_LOCK_CNT) {
338		while (--i >= 0)
339			pli->lock_destroy(locks[i]);
340		abort();
341	}
342
343	for (i = 0; i < RTLD_LOCK_CNT; i++) {
344		if (rtld_locks[i].handle == NULL)
345			continue;
346		if (flags & rtld_locks[i].mask)
347			lockinfo.lock_release(rtld_locks[i].handle);
348		lockinfo.lock_destroy(rtld_locks[i].handle);
349	}
350
351	for (i = 0; i < RTLD_LOCK_CNT; i++) {
352		rtld_locks[i].handle = locks[i];
353		if (flags & rtld_locks[i].mask)
354			pli->wlock_acquire(rtld_locks[i].handle);
355	}
356
357	lockinfo.lock_create = pli->lock_create;
358	lockinfo.lock_destroy = pli->lock_destroy;
359	lockinfo.rlock_acquire = pli->rlock_acquire;
360	lockinfo.wlock_acquire = pli->wlock_acquire;
361	lockinfo.lock_release  = pli->lock_release;
362	lockinfo.thread_set_flag = pli->thread_set_flag;
363	lockinfo.thread_clr_flag = pli->thread_clr_flag;
364	lockinfo.at_fork = pli->at_fork;
365
366	/* restore thread locking state, this time with new locks */
367	thread_mask_clear(~0);
368	thread_mask_set(flags);
369	dbg("_rtld_thread_init: done");
370}
371
372void
373_rtld_atfork_pre(int *locks)
374{
375	RtldLockState ls[2];
376
377	if (locks == NULL)
378		return;
379
380	/*
381	 * Warning: this did not worked well with the rtld compat
382	 * locks above, when the thread signal mask was corrupted (set
383	 * to all signals blocked) if two locks were taken
384	 * simultaneously in the write mode.  The caller of the
385	 * _rtld_atfork_pre() must provide the working implementation
386	 * of the locks anyway, and libthr locks are fine.
387	 */
388	wlock_acquire(rtld_phdr_lock, &ls[0]);
389	wlock_acquire(rtld_bind_lock, &ls[1]);
390
391	/* XXXKIB: I am really sorry for this. */
392	locks[0] = ls[1].lockstate;
393	locks[2] = ls[0].lockstate;
394}
395
396void
397_rtld_atfork_post(int *locks)
398{
399	RtldLockState ls[2];
400
401	if (locks == NULL)
402		return;
403
404	bzero(ls, sizeof(ls));
405	ls[0].lockstate = locks[2];
406	ls[1].lockstate = locks[0];
407	lock_release(rtld_bind_lock, &ls[1]);
408	lock_release(rtld_phdr_lock, &ls[0]);
409}
410