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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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 * Return a pool token given an address
122 _lwkt_token_pool_lookup(void *ptr)
126 i = ((int)(intptr_t)ptr >> 2) ^ ((int)(intptr_t)ptr >> 12);
127 return(&pool_tokens[i & LWKT_MASK_POOL_TOKENS]);
131 * Initialize a tokref_t prior to making it visible in the thread's
136 _lwkt_tokref_init(lwkt_tokref_t ref, lwkt_token_t tok, thread_t td)
140 ref->tr_flags = tok->t_flags;
144 * Obtain all the tokens required by the specified thread on the current
145 * cpu, return 0 on failure and non-zero on success. If a failure occurs
146 * any partially acquired tokens will be released prior to return.
148 * lwkt_getalltokens is called by the LWKT scheduler to acquire all
149 * tokens that the thread had acquired prior to going to sleep.
151 * The scheduler is responsible for maintaining the MP lock count, so
152 * we don't need to deal with tr_flags here.
154 * Called from a critical section.
157 lwkt_getalltokens(thread_t td)
164 * Acquire tokens in forward order, assign or validate tok->t_ref.
166 for (scan = &td->td_toks_base; scan < td->td_toks_stop; ++scan) {
170 * Try to acquire the token if we do not already have
173 * NOTE: If atomic_cmpset_ptr() fails we have to
174 * loop and try again. It just means we
179 if (atomic_cmpset_ptr(&tok->t_ref, NULL, scan))
185 * Test if ref is already recursively held by this
186 * thread. We cannot safely dereference tok->t_ref
187 * (it might belong to another thread and is thus
188 * unstable), but we don't have to. We can simply
191 if (ref >= &td->td_toks_base && ref < td->td_toks_stop)
195 * Otherwise we failed to acquire all the tokens.
198 lwkt_relalltokens(td);
206 * Release all tokens owned by the specified thread on the current cpu.
208 * This code is really simple. Even in cases where we own all the tokens
209 * note that t_ref may not match the scan for recursively held tokens,
210 * or for the case where a lwkt_getalltokens() failed.
212 * The scheduler is responsible for maintaining the MP lock count, so
213 * we don't need to deal with tr_flags here.
215 * Called from a critical section.
218 lwkt_relalltokens(thread_t td)
223 for (scan = &td->td_toks_base; scan < td->td_toks_stop; ++scan) {
225 if (tok->t_ref == scan)
231 * Token acquisition helper function. The caller must have already
232 * made nref visible by adjusting td_toks_stop and will be responsible
233 * for the disposition of nref on either success or failure.
235 * When acquiring tokens recursively we want tok->t_ref to point to
236 * the outer (first) acquisition so it gets cleared only on the last
241 _lwkt_trytokref2(lwkt_tokref_t nref, thread_t td)
246 KKASSERT(td->td_gd->gd_intr_nesting_level == 0);
249 * Make sure the compiler does not reorder prior instructions
250 * beyond this demark.
255 * Attempt to gain ownership
260 * Try to acquire the token if we do not already have
266 * NOTE: If atomic_cmpset_ptr() fails we have to
267 * loop and try again. It just means we
270 if (atomic_cmpset_ptr(&tok->t_ref, NULL, nref))
276 * Test if ref is already recursively held by this
277 * thread. We cannot safely dereference tok->t_ref
278 * (it might belong to another thread and is thus
279 * unstable), but we don't have to. We can simply
282 if (ref >= &td->td_toks_base && ref < td->td_toks_stop)
286 * Otherwise we failed.
293 * Acquire a serializing token. This routine does not block.
297 _lwkt_trytokref(lwkt_tokref_t ref, thread_t td)
299 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0) {
300 if (try_mplock() == 0)
303 if (_lwkt_trytokref2(ref, td) == FALSE) {
305 * Cleanup, deactivate the failed token.
308 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0)
316 * Acquire a serializing token. This routine can block.
320 _lwkt_gettokref(lwkt_tokref_t ref, thread_t td)
322 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0)
324 if (_lwkt_trytokref2(ref, td) == FALSE) {
326 * Give up running if we can't acquire the token right now.
328 * Since the tokref is already active the scheduler now
329 * takes care of acquisition, so we need only call
332 * Since we failed this was not a recursive token so upon
333 * return tr_tok->t_ref should be assigned to this specific
339 KKASSERT(ref->tr_tok->t_ref == ref);
344 lwkt_gettoken(lwkt_token_t tok)
346 thread_t td = curthread;
349 ref = td->td_toks_stop;
350 KKASSERT(ref < &td->td_toks_end);
351 _lwkt_tokref_init(ref, tok, td);
353 _lwkt_gettokref(ref, td);
357 lwkt_getpooltoken(void *ptr)
359 thread_t td = curthread;
363 ref = td->td_toks_stop;
364 KKASSERT(ref < &td->td_toks_end);
365 tok = _lwkt_token_pool_lookup(ptr);
366 _lwkt_tokref_init(ref, tok, td);
368 _lwkt_gettokref(ref, td);
373 lwkt_trytoken(lwkt_token_t tok)
375 thread_t td = curthread;
378 ref = td->td_toks_stop;
379 KKASSERT(ref < &td->td_toks_end);
380 _lwkt_tokref_init(ref, tok, td);
382 return(_lwkt_trytokref(ref, td));
386 * Release a serializing token.
388 * WARNING! All tokens must be released in reverse order. This will be
392 lwkt_reltoken(lwkt_token_t tok)
394 thread_t td = curthread;
398 * Remove ref from thread token list and assert that it matches
399 * the token passed in. Tokens must be released in reverse order.
401 ref = td->td_toks_stop - 1;
402 KKASSERT(ref >= &td->td_toks_base && ref->tr_tok == tok);
403 td->td_toks_stop = ref;
406 * If the token was not MPSAFE release the MP lock.
408 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0)
412 * Make sure the compiler does not reorder the clearing of
418 * Only clear the token if it matches ref. If ref was a recursively
419 * acquired token it may not match.
421 if (tok->t_ref == ref)
426 * Pool tokens are used to provide a type-stable serializing token
427 * pointer that does not race against disappearing data structures.
429 * This routine is called in early boot just after we setup the BSP's
430 * globaldata structure.
433 lwkt_token_pool_init(void)
437 for (i = 0; i < LWKT_NUM_POOL_TOKENS; ++i)
438 lwkt_token_init(&pool_tokens[i], 1);
442 lwkt_token_pool_lookup(void *ptr)
444 return (_lwkt_token_pool_lookup(ptr));
448 * Initialize the owner and release-to cpu to the current cpu
449 * and reset the generation count.
452 lwkt_token_init(lwkt_token_t tok, int mpsafe)
455 tok->t_flags = mpsafe ? LWKT_TOKEN_MPSAFE : 0;
459 lwkt_token_uninit(lwkt_token_t tok)
466 lwkt_token_is_stale(lwkt_tokref_t ref)
468 lwkt_token_t tok = ref->tr_tok;
470 KKASSERT(tok->t_owner == curthread && ref->tr_state == 1 &&
473 /* Token is not stale */
474 if (tok->t_lastowner == tok->t_owner)
478 * The token is stale. Reset to not stale so that the next call to
479 * lwkt_token_is_stale will return "not stale" unless the token
480 * was acquired in-between by another thread.
482 tok->t_lastowner = tok->t_owner;