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
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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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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>
66 #include <vm/vm_param.h>
67 #include <vm/vm_kern.h>
68 #include <vm/vm_object.h>
69 #include <vm/vm_page.h>
70 #include <vm/vm_map.h>
71 #include <vm/vm_pager.h>
72 #include <vm/vm_extern.h>
73 #include <vm/vm_zone.h>
75 #include <machine/stdarg.h>
76 #include <machine/smp.h>
78 #ifndef LWKT_NUM_POOL_TOKENS
79 #define LWKT_NUM_POOL_TOKENS 1024 /* power of 2 */
81 #define LWKT_MASK_POOL_TOKENS (LWKT_NUM_POOL_TOKENS - 1)
84 static int token_debug = 0;
87 static lwkt_token pool_tokens[LWKT_NUM_POOL_TOKENS];
89 #define TOKEN_STRING "REF=%p TOK=%p TD=%p"
90 #define CONTENDED_STRING "REF=%p TOK=%p TD=%p (contention started)"
91 #define UNCONTENDED_STRING "REF=%p TOK=%p TD=%p (contention stopped)"
92 #if !defined(KTR_TOKENS)
93 #define KTR_TOKENS KTR_ALL
96 KTR_INFO_MASTER(tokens);
97 KTR_INFO(KTR_TOKENS, tokens, fail, 0, TOKEN_STRING, sizeof(void *) * 3);
98 KTR_INFO(KTR_TOKENS, tokens, succ, 1, TOKEN_STRING, sizeof(void *) * 3);
100 KTR_INFO(KTR_TOKENS, tokens, release, 2, TOKEN_STRING, sizeof(void *) * 3);
101 KTR_INFO(KTR_TOKENS, tokens, remote, 3, TOKEN_STRING, sizeof(void *) * 3);
102 KTR_INFO(KTR_TOKENS, tokens, reqremote, 4, TOKEN_STRING, sizeof(void *) * 3);
103 KTR_INFO(KTR_TOKENS, tokens, reqfail, 5, TOKEN_STRING, sizeof(void *) * 3);
104 KTR_INFO(KTR_TOKENS, tokens, drain, 6, TOKEN_STRING, sizeof(void *) * 3);
105 KTR_INFO(KTR_TOKENS, tokens, contention_start, 7, CONTENDED_STRING, sizeof(void *) * 3);
106 KTR_INFO(KTR_TOKENS, tokens, contention_stop, 7, UNCONTENDED_STRING, sizeof(void *) * 3);
109 #define logtoken(name, ref) \
110 KTR_LOG(tokens_ ## name, ref, ref->tr_tok, curthread)
113 SYSCTL_INT(_lwkt, OID_AUTO, token_debug, CTLFLAG_RW, &token_debug, 0, "");
117 * Return a pool token given an address
121 _lwkt_token_pool_lookup(void *ptr)
125 i = ((int)(intptr_t)ptr >> 2) ^ ((int)(intptr_t)ptr >> 12);
126 return(&pool_tokens[i & LWKT_MASK_POOL_TOKENS]);
131 * Obtain all the tokens required by the specified thread on the current
132 * cpu, return 0 on failure and non-zero on success.
134 * lwkt_getalltokens is called by the LWKT scheduler to acquire all
135 * tokens that the thread had acquired prior to going to sleep.
137 * Called from a critical section.
140 lwkt_getalltokens(thread_t td)
147 for (scan1 = td->td_toks; scan1; scan1 = scan1->tr_next) {
151 * Try to acquire the token if we do not already have
154 * NOTE: If atomic_cmpset_ptr() fails we have to
155 * loop and try again. It just means we
162 if (atomic_cmpset_ptr(&tok->t_ref, NULL, scan1))
168 * If acquisition fails the token might be held
169 * recursively by another ref owned by the same
172 * NOTE! We cannot just dereference 'ref' to test
173 * the tr_owner as its storage will be
174 * unstable if it belongs to another thread.
176 * NOTE! Since tokens are inserted at the head
177 * of the list we must migrate such tokens
178 * so the actual lock is not cleared until
189 scan2 = scan2->tr_next;
198 * Release all tokens owned by the specified thread on the current cpu.
200 * This code is really simple. Even in cases where we own all the tokens
201 * note that t_ref may not match the scan for recursively held tokens,
202 * or for the case where a lwkt_getalltokens() failed.
204 * Called from a critical section.
207 lwkt_relalltokens(thread_t td)
212 for (scan1 = td->td_toks; scan1; scan1 = scan1->tr_next) {
214 if (tok->t_ref == scan1)
220 * Token acquisition helper function. Note that get/trytokenref do not
221 * reset t_lastowner if the token is already held. Only lwkt_token_is_stale()
222 * is allowed to do that.
224 * NOTE: On failure, this function doesn't remove the token from the
225 * thread's token list, so that you have to perform that yourself:
227 * td->td_toks = ref->tr_next;
231 _lwkt_trytokref2(lwkt_tokref_t nref, thread_t td)
237 KKASSERT(td->td_gd->gd_intr_nesting_level == 0);
240 * Link the tokref into curthread's list. Make sure the
241 * cpu does not reorder these instructions!
243 nref->tr_next = td->td_toks;
249 * Attempt to gain ownership
254 * Try to acquire the token if we do not already have
262 * NOTE: If atomic_cmpset_ptr() fails we have to
263 * loop and try again. It just means we
266 if (atomic_cmpset_ptr(&tok->t_ref, NULL, nref))
272 * If acquisition fails the token might be held
273 * recursively by another ref owned by the same
276 * NOTE! We cannot just dereference 'ref' to test
277 * the tr_owner as its storage will be
278 * unstable if it belongs to another thread.
280 * NOTE! We do not migrate t_ref to nref here as we
281 * want the recursion unwinding in reverse order
282 * to NOT release the token until last the
283 * recursive ref is released.
285 for (scan2 = nref->tr_next; scan2; scan2 = scan2->tr_next) {
294 * Acquire a serializing token. This routine does not block.
298 _lwkt_trytokref(lwkt_tokref_t ref, thread_t td)
300 if (_lwkt_trytokref2(ref, td) == FALSE) {
302 * Cleanup. Remove the token from the thread's list.
304 td->td_toks = ref->tr_next;
311 * Acquire a serializing token. This routine can block.
315 _lwkt_gettokref(lwkt_tokref_t ref, thread_t td)
317 if (_lwkt_trytokref2(ref, td) == FALSE) {
319 * Give up running if we can't acquire the token right now.
320 * But as we have linked in the tokref to the thread's list
321 * (_lwkt_trytokref2), the scheduler now takes care to acquire
322 * the token (by calling lwkt_getalltokens) before resuming
323 * execution. As such, when we return from lwkt_yield(),
324 * the token is acquired.
326 * Since we failed this is not a recursive token so upon
327 * return tr_tok->t_ref should be assigned to this specific
334 if (ref->tr_tok->t_ref != ref) {
336 kprintf("gettokref %p failed, held by tok %p ref %p\n",
337 ref, ref->tr_tok, ref->tr_tok->t_ref);
338 for (scan = td->td_toks; scan; scan = scan->tr_next) {
339 kprintf(" %p\n", scan);
343 KKASSERT(ref->tr_tok->t_ref == ref);
348 lwkt_gettoken(lwkt_tokref_t ref, lwkt_token_t tok)
350 thread_t td = curthread;
352 lwkt_tokref_init(ref, tok, td);
353 _lwkt_gettokref(ref, td);
357 lwkt_getpooltoken(lwkt_tokref_t ref, void *ptr)
359 thread_t td = curthread;
361 lwkt_tokref_init(ref, _lwkt_token_pool_lookup(ptr), td);
362 _lwkt_gettokref(ref, td);
366 lwkt_gettokref(lwkt_tokref_t ref)
368 _lwkt_gettokref(ref, ref->tr_owner);
372 lwkt_trytoken(lwkt_tokref_t ref, lwkt_token_t tok)
374 thread_t td = curthread;
376 lwkt_tokref_init(ref, tok, td);
377 return(_lwkt_trytokref(ref, td));
381 lwkt_trytokref(lwkt_tokref_t ref)
383 return(_lwkt_trytokref(ref, ref->tr_owner));
387 * Release a serializing token.
389 * WARNING! Any recursive tokens must be released in reverse order.
392 lwkt_reltoken(lwkt_tokref_t ref)
394 struct lwkt_tokref **scanp;
401 * Remove the ref from the thread's token list.
403 * NOTE: td == curthread
406 for (scanp = &td->td_toks; *scanp != ref; scanp = &((*scanp)->tr_next))
408 *scanp = ref->tr_next;
412 * Only clear the token if it matches ref. If ref was a recursively
413 * acquired token it may not match.
415 if (tok->t_ref == ref)
420 * Pool tokens are used to provide a type-stable serializing token
421 * pointer that does not race against disappearing data structures.
423 * This routine is called in early boot just after we setup the BSP's
424 * globaldata structure.
427 lwkt_token_pool_init(void)
431 for (i = 0; i < LWKT_NUM_POOL_TOKENS; ++i)
432 lwkt_token_init(&pool_tokens[i]);
436 lwkt_token_pool_lookup(void *ptr)
438 return (_lwkt_token_pool_lookup(ptr));
442 * Initialize the owner and release-to cpu to the current cpu
443 * and reset the generation count.
446 lwkt_token_init(lwkt_token_t tok)
452 lwkt_token_uninit(lwkt_token_t tok)
459 lwkt_token_is_stale(lwkt_tokref_t ref)
461 lwkt_token_t tok = ref->tr_tok;
463 KKASSERT(tok->t_owner == curthread && ref->tr_state == 1 &&
466 /* Token is not stale */
467 if (tok->t_lastowner == tok->t_owner)
471 * The token is stale. Reset to not stale so that the next call to
472 * lwkt_token_is_stale will return "not stale" unless the token
473 * was acquired in-between by another thread.
475 tok->t_lastowner = tok->t_owner;