rtld_lock.c revision 281453 
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 281453 2015-04-12 06:45:40Z 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 implement
42 * using assembly language sequences in "rtld_start.S".
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;
68
69static void *
70def_lock_create()
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 = (Lock *)lock;
121    sigset_t tmp_oldsigmask;
122
123    for ( ; ; ) {
124	sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask);
125	if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG))
126	    break;
127	sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
128    }
129    oldsigmask = tmp_oldsigmask;
130}
131
132static void
133def_lock_release(void *lock)
134{
135    Lock *l = (Lock *)lock;
136
137    if ((l->lock & WAFLAG) == 0)
138    	atomic_add_rel_int(&l->lock, -RC_INCR);
139    else {
140    	atomic_add_rel_int(&l->lock, -WAFLAG);
141    	sigprocmask(SIG_SETMASK, &oldsigmask, NULL);
142    }
143}
144
145static int
146def_thread_set_flag(int mask)
147{
148	int old_val = thread_flag;
149	thread_flag |= mask;
150	return (old_val);
151}
152
153static int
154def_thread_clr_flag(int mask)
155{
156	int old_val = thread_flag;
157	thread_flag &= ~mask;
158	return (old_val);
159}
160
161/*
162 * Public interface exposed to the rest of the dynamic linker.
163 */
164static struct RtldLockInfo lockinfo;
165static struct RtldLockInfo deflockinfo;
166
167static __inline int
168thread_mask_set(int mask)
169{
170	return lockinfo.thread_set_flag(mask);
171}
172
173static __inline void
174thread_mask_clear(int mask)
175{
176	lockinfo.thread_clr_flag(mask);
177}
178
179#define	RTLD_LOCK_CNT	3
180struct rtld_lock {
181	void	*handle;
182	int	 mask;
183} rtld_locks[RTLD_LOCK_CNT];
184
185rtld_lock_t	rtld_bind_lock = &rtld_locks[0];
186rtld_lock_t	rtld_libc_lock = &rtld_locks[1];
187rtld_lock_t	rtld_phdr_lock = &rtld_locks[2];
188
189void
190rlock_acquire(rtld_lock_t lock, RtldLockState *lockstate)
191{
192
193	if (lockstate == NULL)
194		return;
195
196	if (thread_mask_set(lock->mask) & lock->mask) {
197		dbg("rlock_acquire: recursed");
198		lockstate->lockstate = RTLD_LOCK_UNLOCKED;
199		return;
200	}
201	lockinfo.rlock_acquire(lock->handle);
202	lockstate->lockstate = RTLD_LOCK_RLOCKED;
203}
204
205void
206wlock_acquire(rtld_lock_t lock, RtldLockState *lockstate)
207{
208
209	if (lockstate == NULL)
210		return;
211
212	if (thread_mask_set(lock->mask) & lock->mask) {
213		dbg("wlock_acquire: recursed");
214		lockstate->lockstate = RTLD_LOCK_UNLOCKED;
215		return;
216	}
217	lockinfo.wlock_acquire(lock->handle);
218	lockstate->lockstate = RTLD_LOCK_WLOCKED;
219}
220
221void
222lock_release(rtld_lock_t lock, RtldLockState *lockstate)
223{
224
225	if (lockstate == NULL)
226		return;
227
228	switch (lockstate->lockstate) {
229	case RTLD_LOCK_UNLOCKED:
230		break;
231	case RTLD_LOCK_RLOCKED:
232	case RTLD_LOCK_WLOCKED:
233		thread_mask_clear(lock->mask);
234		lockinfo.lock_release(lock->handle);
235		break;
236	default:
237		assert(0);
238	}
239}
240
241void
242lock_upgrade(rtld_lock_t lock, RtldLockState *lockstate)
243{
244
245	if (lockstate == NULL)
246		return;
247
248	lock_release(lock, lockstate);
249	wlock_acquire(lock, lockstate);
250}
251
252void
253lock_restart_for_upgrade(RtldLockState *lockstate)
254{
255
256	if (lockstate == NULL)
257		return;
258
259	switch (lockstate->lockstate) {
260	case RTLD_LOCK_UNLOCKED:
261	case RTLD_LOCK_WLOCKED:
262		break;
263	case RTLD_LOCK_RLOCKED:
264		siglongjmp(lockstate->env, 1);
265		break;
266	default:
267		assert(0);
268	}
269}
270
271void
272lockdflt_init()
273{
274    int i;
275
276    deflockinfo.rtli_version  = RTLI_VERSION;
277    deflockinfo.lock_create   = def_lock_create;
278    deflockinfo.lock_destroy  = def_lock_destroy;
279    deflockinfo.rlock_acquire = def_rlock_acquire;
280    deflockinfo.wlock_acquire = def_wlock_acquire;
281    deflockinfo.lock_release  = def_lock_release;
282    deflockinfo.thread_set_flag = def_thread_set_flag;
283    deflockinfo.thread_clr_flag = def_thread_clr_flag;
284    deflockinfo.at_fork = NULL;
285
286    for (i = 0; i < RTLD_LOCK_CNT; i++) {
287	    rtld_locks[i].mask   = (1 << i);
288	    rtld_locks[i].handle = NULL;
289    }
290
291    memcpy(&lockinfo, &deflockinfo, sizeof(lockinfo));
292    _rtld_thread_init(NULL);
293    /*
294     * Construct a mask to block all signals except traps which might
295     * conceivably be generated within the dynamic linker itself.
296     */
297    sigfillset(&fullsigmask);
298    sigdelset(&fullsigmask, SIGILL);
299    sigdelset(&fullsigmask, SIGTRAP);
300    sigdelset(&fullsigmask, SIGABRT);
301    sigdelset(&fullsigmask, SIGEMT);
302    sigdelset(&fullsigmask, SIGFPE);
303    sigdelset(&fullsigmask, SIGBUS);
304    sigdelset(&fullsigmask, SIGSEGV);
305    sigdelset(&fullsigmask, SIGSYS);
306}
307
308/*
309 * Callback function to allow threads implementation to
310 * register their own locking primitives if the default
311 * one is not suitable.
312 * The current context should be the only context
313 * executing at the invocation time.
314 */
315void
316_rtld_thread_init(struct RtldLockInfo *pli)
317{
318	int flags, i;
319	void *locks[RTLD_LOCK_CNT];
320
321	/* disable all locking while this function is running */
322	flags =	thread_mask_set(~0);
323
324	if (pli == NULL)
325		pli = &deflockinfo;
326
327
328	for (i = 0; i < RTLD_LOCK_CNT; i++)
329		if ((locks[i] = pli->lock_create()) == NULL)
330			break;
331
332	if (i < RTLD_LOCK_CNT) {
333		while (--i >= 0)
334			pli->lock_destroy(locks[i]);
335		abort();
336	}
337
338	for (i = 0; i < RTLD_LOCK_CNT; i++) {
339		if (rtld_locks[i].handle == NULL)
340			continue;
341		if (flags & rtld_locks[i].mask)
342			lockinfo.lock_release(rtld_locks[i].handle);
343		lockinfo.lock_destroy(rtld_locks[i].handle);
344	}
345
346	for (i = 0; i < RTLD_LOCK_CNT; i++) {
347		rtld_locks[i].handle = locks[i];
348		if (flags & rtld_locks[i].mask)
349			pli->wlock_acquire(rtld_locks[i].handle);
350	}
351
352	lockinfo.lock_create = pli->lock_create;
353	lockinfo.lock_destroy = pli->lock_destroy;
354	lockinfo.rlock_acquire = pli->rlock_acquire;
355	lockinfo.wlock_acquire = pli->wlock_acquire;
356	lockinfo.lock_release  = pli->lock_release;
357	lockinfo.thread_set_flag = pli->thread_set_flag;
358	lockinfo.thread_clr_flag = pli->thread_clr_flag;
359	lockinfo.at_fork = pli->at_fork;
360
361	/* restore thread locking state, this time with new locks */
362	thread_mask_clear(~0);
363	thread_mask_set(flags);
364	dbg("_rtld_thread_init: done");
365}
366
367void
368_rtld_atfork_pre(int *locks)
369{
370	RtldLockState ls[2];
371
372	if (locks == NULL)
373		return;
374
375	/*
376	 * Warning: this does not work with the rtld compat locks
377	 * above, since the thread signal mask is corrupted (set to
378	 * all signals blocked) if two locks are taken in write mode.
379	 * The caller of the _rtld_atfork_pre() must provide the
380	 * working implementation of the locks, and libthr locks are
381	 * fine.
382	 */
383	wlock_acquire(rtld_phdr_lock, &ls[0]);
384	wlock_acquire(rtld_bind_lock, &ls[1]);
385
386	/* XXXKIB: I am really sorry for this. */
387	locks[0] = ls[1].lockstate;
388	locks[2] = ls[0].lockstate;
389}
390
391void
392_rtld_atfork_post(int *locks)
393{
394	RtldLockState ls[2];
395
396	if (locks == NULL)
397		return;
398
399	bzero(ls, sizeof(ls));
400	ls[0].lockstate = locks[2];
401	ls[1].lockstate = locks[0];
402	lock_release(rtld_bind_lock, &ls[1]);
403	lock_release(rtld_phdr_lock, &ls[0]);
404}
405