2 * Copyright (c) 2003,2004,2009 The DragonFly Project. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in
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21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 * lwkt_token - Implement soft token locks.
38 * Tokens are locks which serialize a thread only while the thread is
39 * running. If the thread blocks all tokens are released, then reacquired
40 * when the thread resumes.
42 * This implementation requires no critical sections or spin locks, but
43 * does use atomic_cmpset_ptr().
45 * Tokens may be recursively acquired by the same thread. However the
46 * caller must be sure to release such tokens in reverse order.
48 #include <sys/param.h>
49 #include <sys/systm.h>
50 #include <sys/kernel.h>
52 #include <sys/rtprio.h>
53 #include <sys/queue.h>
54 #include <sys/sysctl.h>
56 #include <sys/kthread.h>
57 #include <machine/cpu.h>
60 #include <sys/spinlock.h>
62 #include <sys/thread2.h>
63 #include <sys/spinlock2.h>
64 #include <sys/mplock2.h>
67 #include <vm/vm_param.h>
68 #include <vm/vm_kern.h>
69 #include <vm/vm_object.h>
70 #include <vm/vm_page.h>
71 #include <vm/vm_map.h>
72 #include <vm/vm_pager.h>
73 #include <vm/vm_extern.h>
74 #include <vm/vm_zone.h>
76 #include <machine/stdarg.h>
77 #include <machine/smp.h>
79 #ifndef LWKT_NUM_POOL_TOKENS
80 #define LWKT_NUM_POOL_TOKENS 1024 /* power of 2 */
82 #define LWKT_MASK_POOL_TOKENS (LWKT_NUM_POOL_TOKENS - 1)
85 static int token_debug = 0;
88 static lwkt_token pool_tokens[LWKT_NUM_POOL_TOKENS];
90 #define TOKEN_STRING "REF=%p TOK=%p TD=%p"
91 #define CONTENDED_STRING "REF=%p TOK=%p TD=%p (contention started)"
92 #define UNCONTENDED_STRING "REF=%p TOK=%p TD=%p (contention stopped)"
93 #if !defined(KTR_TOKENS)
94 #define KTR_TOKENS KTR_ALL
97 KTR_INFO_MASTER(tokens);
98 KTR_INFO(KTR_TOKENS, tokens, fail, 0, TOKEN_STRING, sizeof(void *) * 3);
99 KTR_INFO(KTR_TOKENS, tokens, succ, 1, TOKEN_STRING, sizeof(void *) * 3);
101 KTR_INFO(KTR_TOKENS, tokens, release, 2, TOKEN_STRING, sizeof(void *) * 3);
102 KTR_INFO(KTR_TOKENS, tokens, remote, 3, TOKEN_STRING, sizeof(void *) * 3);
103 KTR_INFO(KTR_TOKENS, tokens, reqremote, 4, TOKEN_STRING, sizeof(void *) * 3);
104 KTR_INFO(KTR_TOKENS, tokens, reqfail, 5, TOKEN_STRING, sizeof(void *) * 3);
105 KTR_INFO(KTR_TOKENS, tokens, drain, 6, TOKEN_STRING, sizeof(void *) * 3);
106 KTR_INFO(KTR_TOKENS, tokens, contention_start, 7, CONTENDED_STRING, sizeof(void *) * 3);
107 KTR_INFO(KTR_TOKENS, tokens, contention_stop, 7, UNCONTENDED_STRING, sizeof(void *) * 3);
110 #define logtoken(name, ref) \
111 KTR_LOG(tokens_ ## name, ref, ref->tr_tok, curthread)
114 SYSCTL_INT(_lwkt, OID_AUTO, token_debug, CTLFLAG_RW, &token_debug, 0, "");
118 * Global tokens. These replace the MP lock for major subsystem locking.
119 * These tokens are initially used to lockup both global and individual
122 * Once individual structures get their own locks these tokens are used
123 * only to protect global lists & other variables and to interlock
124 * allocations and teardowns and such.
126 * The UP initializer causes token acquisition to also acquire the MP lock
127 * for maximum compatibility. The feature may be enabled and disabled at
128 * any time, the MP state is copied to the tokref when the token is acquired
129 * and will not race against sysctl changes.
131 struct lwkt_token pmap_token = LWKT_TOKEN_UP_INITIALIZER(pmap_token);
132 struct lwkt_token dev_token = LWKT_TOKEN_UP_INITIALIZER(dev_token);
133 struct lwkt_token vm_token = LWKT_TOKEN_UP_INITIALIZER(vm_token);
134 struct lwkt_token vmspace_token = LWKT_TOKEN_UP_INITIALIZER(vmspace_token);
135 struct lwkt_token kvm_token = LWKT_TOKEN_UP_INITIALIZER(kvm_token);
136 struct lwkt_token proc_token = LWKT_TOKEN_UP_INITIALIZER(proc_token);
137 struct lwkt_token tty_token = LWKT_TOKEN_UP_INITIALIZER(tty_token);
138 struct lwkt_token vnode_token = LWKT_TOKEN_UP_INITIALIZER(vnode_token);
139 struct lwkt_token vmobj_token = LWKT_TOKEN_UP_INITIALIZER(vmobj_token);
141 SYSCTL_INT(_lwkt, OID_AUTO, pmap_mpsafe,
142 CTLFLAG_RW, &pmap_token.t_flags, 0, "");
143 SYSCTL_INT(_lwkt, OID_AUTO, dev_mpsafe,
144 CTLFLAG_RW, &dev_token.t_flags, 0, "");
145 SYSCTL_INT(_lwkt, OID_AUTO, vm_mpsafe,
146 CTLFLAG_RW, &vm_token.t_flags, 0, "");
147 SYSCTL_INT(_lwkt, OID_AUTO, vmspace_mpsafe,
148 CTLFLAG_RW, &vmspace_token.t_flags, 0, "");
149 SYSCTL_INT(_lwkt, OID_AUTO, kvm_mpsafe,
150 CTLFLAG_RW, &kvm_token.t_flags, 0, "");
151 SYSCTL_INT(_lwkt, OID_AUTO, proc_mpsafe,
152 CTLFLAG_RW, &proc_token.t_flags, 0, "");
153 SYSCTL_INT(_lwkt, OID_AUTO, tty_mpsafe,
154 CTLFLAG_RW, &tty_token.t_flags, 0, "");
155 SYSCTL_INT(_lwkt, OID_AUTO, vnode_mpsafe,
156 CTLFLAG_RW, &vnode_token.t_flags, 0, "");
157 SYSCTL_INT(_lwkt, OID_AUTO, vmobj_mpsafe,
158 CTLFLAG_RW, &vmobj_token.t_flags, 0, "");
161 * The collision count is bumped every time the LWKT scheduler fails
162 * to acquire needed tokens in addition to a normal lwkt_gettoken()
165 SYSCTL_LONG(_lwkt, OID_AUTO, pmap_collisions,
166 CTLFLAG_RW, &pmap_token.t_collisions, 0, "");
167 SYSCTL_LONG(_lwkt, OID_AUTO, dev_collisions,
168 CTLFLAG_RW, &dev_token.t_collisions, 0, "");
169 SYSCTL_LONG(_lwkt, OID_AUTO, vm_collisions,
170 CTLFLAG_RW, &vm_token.t_collisions, 0, "");
171 SYSCTL_LONG(_lwkt, OID_AUTO, vmspace_collisions,
172 CTLFLAG_RW, &vmspace_token.t_collisions, 0, "");
173 SYSCTL_LONG(_lwkt, OID_AUTO, kvm_collisions,
174 CTLFLAG_RW, &kvm_token.t_collisions, 0, "");
175 SYSCTL_LONG(_lwkt, OID_AUTO, proc_collisions,
176 CTLFLAG_RW, &proc_token.t_collisions, 0, "");
177 SYSCTL_LONG(_lwkt, OID_AUTO, tty_collisions,
178 CTLFLAG_RW, &tty_token.t_collisions, 0, "");
179 SYSCTL_LONG(_lwkt, OID_AUTO, vnode_collisions,
180 CTLFLAG_RW, &vnode_token.t_collisions, 0, "");
183 * Return a pool token given an address
187 _lwkt_token_pool_lookup(void *ptr)
191 i = ((int)(intptr_t)ptr >> 2) ^ ((int)(intptr_t)ptr >> 12);
192 return(&pool_tokens[i & LWKT_MASK_POOL_TOKENS]);
196 * Initialize a tokref_t prior to making it visible in the thread's
199 * As an optimization we set the MPSAFE flag if the thread is already
200 * holding the MP lock. This bypasses unncessary calls to get_mplock() and
201 * rel_mplock() on tokens which are not normally MPSAFE when the thread
202 * is already holding the MP lock.
204 * WARNING: The inherited td_xpcount does not count here because a switch
205 * could schedule the preempted thread and blow away the inherited
210 _lwkt_tokref_init(lwkt_tokref_t ref, lwkt_token_t tok, thread_t td)
214 ref->tr_flags = tok->t_flags;
218 ref->tr_flags |= LWKT_TOKEN_MPSAFE;
222 * Obtain all the tokens required by the specified thread on the current
223 * cpu, return 0 on failure and non-zero on success. If a failure occurs
224 * any partially acquired tokens will be released prior to return.
226 * lwkt_getalltokens is called by the LWKT scheduler to acquire all
227 * tokens that the thread had acquired prior to going to sleep.
229 * The scheduler is responsible for maintaining the MP lock count, so
230 * we don't need to deal with tr_flags here. We also do not do any
231 * logging here. The logging done by lwkt_gettoken() is plenty good
232 * enough to get a feel for it.
234 * Called from a critical section.
237 lwkt_getalltokens(thread_t td, const char **msgp, const void **addrp)
244 * Acquire tokens in forward order, assign or validate tok->t_ref.
246 for (scan = &td->td_toks_base; scan < td->td_toks_stop; ++scan) {
250 * Try to acquire the token if we do not already have
253 * NOTE: If atomic_cmpset_ptr() fails we have to
254 * loop and try again. It just means we
259 if (atomic_cmpset_ptr(&tok->t_ref, NULL, scan))
265 * Test if ref is already recursively held by this
266 * thread. We cannot safely dereference tok->t_ref
267 * (it might belong to another thread and is thus
268 * unstable), but we don't have to. We can simply
271 if (ref >= &td->td_toks_base && ref < td->td_toks_stop)
275 * Otherwise we failed to acquire all the tokens.
279 *addrp = scan->tr_stallpc;
280 atomic_add_long(&tok->t_collisions, 1);
281 lwkt_relalltokens(td);
289 * Release all tokens owned by the specified thread on the current cpu.
291 * This code is really simple. Even in cases where we own all the tokens
292 * note that t_ref may not match the scan for recursively held tokens,
293 * or for the case where a lwkt_getalltokens() failed.
295 * The scheduler is responsible for maintaining the MP lock count, so
296 * we don't need to deal with tr_flags here.
298 * Called from a critical section.
301 lwkt_relalltokens(thread_t td)
306 for (scan = &td->td_toks_base; scan < td->td_toks_stop; ++scan) {
308 if (tok->t_ref == scan)
314 * Token acquisition helper function. The caller must have already
315 * made nref visible by adjusting td_toks_stop and will be responsible
316 * for the disposition of nref on either success or failure.
318 * When acquiring tokens recursively we want tok->t_ref to point to
319 * the outer (first) acquisition so it gets cleared only on the last
324 _lwkt_trytokref2(lwkt_tokref_t nref, thread_t td, int blocking)
330 * Make sure the compiler does not reorder prior instructions
331 * beyond this demark.
336 * Attempt to gain ownership
341 * Try to acquire the token if we do not already have
342 * it. This is not allowed if we are in a hard code
343 * section (because it 'might' have blocked).
347 KASSERT((blocking == 0 ||
348 td->td_gd->gd_intr_nesting_level == 0 ||
349 panic_cpu_gd == mycpu),
350 ("Attempt to acquire token %p not already "
351 "held in hard code section", tok));
354 * NOTE: If atomic_cmpset_ptr() fails we have to
355 * loop and try again. It just means we
358 if (atomic_cmpset_ptr(&tok->t_ref, NULL, nref))
364 * Test if ref is already recursively held by this
365 * thread. We cannot safely dereference tok->t_ref
366 * (it might belong to another thread and is thus
367 * unstable), but we don't have to. We can simply
370 * It is ok to acquire a token that is already held
371 * by the current thread when in a hard code section.
373 if (ref >= &td->td_toks_base && ref < td->td_toks_stop)
377 * Otherwise we failed, and it is not ok to attempt to
378 * acquire a token in a hard code section.
380 KASSERT((blocking == 0 ||
381 td->td_gd->gd_intr_nesting_level == 0),
382 ("Attempt to acquire token %p not already "
383 "held in hard code section", tok));
390 * Acquire a serializing token. This routine does not block.
394 _lwkt_trytokref(lwkt_tokref_t ref, thread_t td)
396 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0) {
397 if (try_mplock() == 0) {
402 if (_lwkt_trytokref2(ref, td, 0) == FALSE) {
404 * Cleanup, deactivate the failed token.
406 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0)
415 * Acquire a serializing token. This routine can block.
419 _lwkt_gettokref(lwkt_tokref_t ref, thread_t td, const void **stkframe)
421 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0)
423 if (_lwkt_trytokref2(ref, td, 1) == FALSE) {
425 * Give up running if we can't acquire the token right now.
427 * Since the tokref is already active the scheduler now
428 * takes care of acquisition, so we need only call
431 * Since we failed this was not a recursive token so upon
432 * return tr_tok->t_ref should be assigned to this specific
435 ref->tr_stallpc = stkframe[-1];
436 atomic_add_long(&ref->tr_tok->t_collisions, 1);
440 KKASSERT(ref->tr_tok->t_ref == ref);
445 lwkt_gettoken(lwkt_token_t tok)
447 thread_t td = curthread;
450 ref = td->td_toks_stop;
451 KKASSERT(ref < &td->td_toks_end);
453 _lwkt_tokref_init(ref, tok, td);
454 _lwkt_gettokref(ref, td, (const void **)&tok);
458 lwkt_gettoken_hard(lwkt_token_t tok)
460 thread_t td = curthread;
463 ref = td->td_toks_stop;
464 KKASSERT(ref < &td->td_toks_end);
466 _lwkt_tokref_init(ref, tok, td);
467 _lwkt_gettokref(ref, td, (const void **)&tok);
468 crit_enter_hard_gd(td->td_gd);
472 lwkt_getpooltoken(void *ptr)
474 thread_t td = curthread;
478 ref = td->td_toks_stop;
479 KKASSERT(ref < &td->td_toks_end);
481 tok = _lwkt_token_pool_lookup(ptr);
482 _lwkt_tokref_init(ref, tok, td);
483 _lwkt_gettokref(ref, td, (const void **)&ptr);
488 lwkt_trytoken(lwkt_token_t tok)
490 thread_t td = curthread;
493 ref = td->td_toks_stop;
494 KKASSERT(ref < &td->td_toks_end);
496 _lwkt_tokref_init(ref, tok, td);
497 return(_lwkt_trytokref(ref, td));
501 * Release a serializing token.
503 * WARNING! All tokens must be released in reverse order. This will be
507 lwkt_reltoken(lwkt_token_t tok)
509 thread_t td = curthread;
513 * Remove ref from thread token list and assert that it matches
514 * the token passed in. Tokens must be released in reverse order.
516 ref = td->td_toks_stop - 1;
517 KKASSERT(ref >= &td->td_toks_base && ref->tr_tok == tok);
520 * If the token was not MPSAFE release the MP lock.
522 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0)
524 td->td_toks_stop = ref;
527 * Make sure the compiler does not reorder the clearing of
533 * Only clear the token if it matches ref. If ref was a recursively
534 * acquired token it may not match.
536 if (tok->t_ref == ref)
541 lwkt_reltoken_hard(lwkt_token_t tok)
548 * Pool tokens are used to provide a type-stable serializing token
549 * pointer that does not race against disappearing data structures.
551 * This routine is called in early boot just after we setup the BSP's
552 * globaldata structure.
555 lwkt_token_pool_init(void)
559 for (i = 0; i < LWKT_NUM_POOL_TOKENS; ++i)
560 lwkt_token_init(&pool_tokens[i], 1, "pool");
564 lwkt_token_pool_lookup(void *ptr)
566 return (_lwkt_token_pool_lookup(ptr));
570 * Initialize a token. If mpsafe is 0, the MP lock is acquired before
571 * acquiring the token and released after releasing the token.
574 lwkt_token_init(lwkt_token_t tok, int mpsafe, const char *desc)
577 tok->t_flags = mpsafe ? LWKT_TOKEN_MPSAFE : 0;
578 tok->t_collisions = 0;
583 lwkt_token_uninit(lwkt_token_t tok)
590 lwkt_token_is_stale(lwkt_tokref_t ref)
592 lwkt_token_t tok = ref->tr_tok;
594 KKASSERT(tok->t_owner == curthread && ref->tr_state == 1 &&
597 /* Token is not stale */
598 if (tok->t_lastowner == tok->t_owner)
602 * The token is stale. Reset to not stale so that the next call to
603 * lwkt_token_is_stale will return "not stale" unless the token
604 * was acquired in-between by another thread.
606 tok->t_lastowner = tok->t_owner;