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
15 * the documentation and/or other materials provided with the
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18 * contributors may be used to endorse or promote products derived
19 * from this software without specific, prior written permission.
21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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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;
132 struct lwkt_token dev_token = LWKT_TOKEN_UP_INITIALIZER;
133 struct lwkt_token vm_token = LWKT_TOKEN_UP_INITIALIZER;
134 struct lwkt_token vmspace_token = LWKT_TOKEN_UP_INITIALIZER;
135 struct lwkt_token kvm_token = LWKT_TOKEN_UP_INITIALIZER;
136 struct lwkt_token proc_token = LWKT_TOKEN_UP_INITIALIZER;
137 struct lwkt_token tty_token = LWKT_TOKEN_UP_INITIALIZER;
138 struct lwkt_token vnode_token = LWKT_TOKEN_UP_INITIALIZER;
140 SYSCTL_INT(_lwkt, OID_AUTO, pmap_mpsafe,
141 CTLFLAG_RW, &pmap_token.t_flags, 0, "");
142 SYSCTL_INT(_lwkt, OID_AUTO, dev_mpsafe,
143 CTLFLAG_RW, &dev_token.t_flags, 0, "");
144 SYSCTL_INT(_lwkt, OID_AUTO, vm_mpsafe,
145 CTLFLAG_RW, &vm_token.t_flags, 0, "");
146 SYSCTL_INT(_lwkt, OID_AUTO, vmspace_mpsafe,
147 CTLFLAG_RW, &vmspace_token.t_flags, 0, "");
148 SYSCTL_INT(_lwkt, OID_AUTO, kvm_mpsafe,
149 CTLFLAG_RW, &kvm_token.t_flags, 0, "");
150 SYSCTL_INT(_lwkt, OID_AUTO, proc_mpsafe,
151 CTLFLAG_RW, &proc_token.t_flags, 0, "");
152 SYSCTL_INT(_lwkt, OID_AUTO, tty_mpsafe,
153 CTLFLAG_RW, &tty_token.t_flags, 0, "");
154 SYSCTL_INT(_lwkt, OID_AUTO, vnode_mpsafe,
155 CTLFLAG_RW, &vnode_token.t_flags, 0, "");
158 * The collision count is bumped every time the LWKT scheduler fails
159 * to acquire needed tokens in addition to a normal lwkt_gettoken()
162 SYSCTL_LONG(_lwkt, OID_AUTO, pmap_collisions,
163 CTLFLAG_RW, &pmap_token.t_collisions, 0, "");
164 SYSCTL_LONG(_lwkt, OID_AUTO, dev_collisions,
165 CTLFLAG_RW, &dev_token.t_collisions, 0, "");
166 SYSCTL_LONG(_lwkt, OID_AUTO, vm_collisions,
167 CTLFLAG_RW, &vm_token.t_collisions, 0, "");
168 SYSCTL_LONG(_lwkt, OID_AUTO, vmspace_collisions,
169 CTLFLAG_RW, &vmspace_token.t_collisions, 0, "");
170 SYSCTL_LONG(_lwkt, OID_AUTO, kvm_collisions,
171 CTLFLAG_RW, &kvm_token.t_collisions, 0, "");
172 SYSCTL_LONG(_lwkt, OID_AUTO, proc_collisions,
173 CTLFLAG_RW, &proc_token.t_collisions, 0, "");
174 SYSCTL_LONG(_lwkt, OID_AUTO, tty_collisions,
175 CTLFLAG_RW, &tty_token.t_collisions, 0, "");
176 SYSCTL_LONG(_lwkt, OID_AUTO, vnode_collisions,
177 CTLFLAG_RW, &vnode_token.t_collisions, 0, "");
180 * Return a pool token given an address
184 _lwkt_token_pool_lookup(void *ptr)
188 i = ((int)(intptr_t)ptr >> 2) ^ ((int)(intptr_t)ptr >> 12);
189 return(&pool_tokens[i & LWKT_MASK_POOL_TOKENS]);
193 * Initialize a tokref_t prior to making it visible in the thread's
196 * As an optimization we set the MPSAFE flag if the thread is already
197 * holding the MP lock. This bypasses unncessary calls to get_mplock() and
198 * rel_mplock() on tokens which are not normally MPSAFE when the thread
199 * is already holding the MP lock.
203 _lwkt_tokref_init(lwkt_tokref_t ref, lwkt_token_t tok, thread_t td)
207 ref->tr_flags = tok->t_flags;
211 ref->tr_flags |= LWKT_TOKEN_MPSAFE;
215 * Obtain all the tokens required by the specified thread on the current
216 * cpu, return 0 on failure and non-zero on success. If a failure occurs
217 * any partially acquired tokens will be released prior to return.
219 * lwkt_getalltokens is called by the LWKT scheduler to acquire all
220 * tokens that the thread had acquired prior to going to sleep.
222 * The scheduler is responsible for maintaining the MP lock count, so
223 * we don't need to deal with tr_flags here. We also do not do any
224 * logging here. The logging done by lwkt_gettoken() is plenty good
225 * enough to get a feel for it.
227 * Called from a critical section.
230 lwkt_getalltokens(thread_t td, const char **msgp, const void **addrp)
237 * Acquire tokens in forward order, assign or validate tok->t_ref.
239 for (scan = &td->td_toks_base; scan < td->td_toks_stop; ++scan) {
243 * Try to acquire the token if we do not already have
246 * NOTE: If atomic_cmpset_ptr() fails we have to
247 * loop and try again. It just means we
252 if (atomic_cmpset_ptr(&tok->t_ref, NULL, scan))
258 * Test if ref is already recursively held by this
259 * thread. We cannot safely dereference tok->t_ref
260 * (it might belong to another thread and is thus
261 * unstable), but we don't have to. We can simply
264 if (ref >= &td->td_toks_base && ref < td->td_toks_stop)
268 * Otherwise we failed to acquire all the tokens.
272 *addrp = scan->tr_stallpc;
273 atomic_add_long(&tok->t_collisions, 1);
274 lwkt_relalltokens(td);
282 * Release all tokens owned by the specified thread on the current cpu.
284 * This code is really simple. Even in cases where we own all the tokens
285 * note that t_ref may not match the scan for recursively held tokens,
286 * or for the case where a lwkt_getalltokens() failed.
288 * The scheduler is responsible for maintaining the MP lock count, so
289 * we don't need to deal with tr_flags here.
291 * Called from a critical section.
294 lwkt_relalltokens(thread_t td)
299 for (scan = &td->td_toks_base; scan < td->td_toks_stop; ++scan) {
301 if (tok->t_ref == scan)
307 * Token acquisition helper function. The caller must have already
308 * made nref visible by adjusting td_toks_stop and will be responsible
309 * for the disposition of nref on either success or failure.
311 * When acquiring tokens recursively we want tok->t_ref to point to
312 * the outer (first) acquisition so it gets cleared only on the last
317 _lwkt_trytokref2(lwkt_tokref_t nref, thread_t td)
322 KKASSERT(td->td_gd->gd_intr_nesting_level == 0);
325 * Make sure the compiler does not reorder prior instructions
326 * beyond this demark.
331 * Attempt to gain ownership
336 * Try to acquire the token if we do not already have
342 * NOTE: If atomic_cmpset_ptr() fails we have to
343 * loop and try again. It just means we
346 if (atomic_cmpset_ptr(&tok->t_ref, NULL, nref))
352 * Test if ref is already recursively held by this
353 * thread. We cannot safely dereference tok->t_ref
354 * (it might belong to another thread and is thus
355 * unstable), but we don't have to. We can simply
358 if (ref >= &td->td_toks_base && ref < td->td_toks_stop)
362 * Otherwise we failed.
369 * Acquire a serializing token. This routine does not block.
373 _lwkt_trytokref(lwkt_tokref_t ref, thread_t td)
375 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0) {
376 if (try_mplock() == 0)
379 if (_lwkt_trytokref2(ref, td) == FALSE) {
381 * Cleanup, deactivate the failed token.
384 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0)
392 * Acquire a serializing token. This routine can block.
396 _lwkt_gettokref(lwkt_tokref_t ref, thread_t td, const void **stkframe)
398 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0)
400 if (_lwkt_trytokref2(ref, td) == FALSE) {
402 * Give up running if we can't acquire the token right now.
404 * Since the tokref is already active the scheduler now
405 * takes care of acquisition, so we need only call
408 * Since we failed this was not a recursive token so upon
409 * return tr_tok->t_ref should be assigned to this specific
412 ref->tr_stallpc = stkframe[-1];
413 atomic_add_long(&ref->tr_tok->t_collisions, 1);
417 KKASSERT(ref->tr_tok->t_ref == ref);
422 lwkt_gettoken(lwkt_token_t tok)
424 thread_t td = curthread;
427 ref = td->td_toks_stop;
428 KKASSERT(ref < &td->td_toks_end);
429 _lwkt_tokref_init(ref, tok, td);
431 _lwkt_gettokref(ref, td, (const void **)&tok);
435 lwkt_getpooltoken(void *ptr)
437 thread_t td = curthread;
441 ref = td->td_toks_stop;
442 KKASSERT(ref < &td->td_toks_end);
443 tok = _lwkt_token_pool_lookup(ptr);
444 _lwkt_tokref_init(ref, tok, td);
446 _lwkt_gettokref(ref, td, (const void **)&ptr);
451 lwkt_trytoken(lwkt_token_t tok)
453 thread_t td = curthread;
456 ref = td->td_toks_stop;
457 KKASSERT(ref < &td->td_toks_end);
458 _lwkt_tokref_init(ref, tok, td);
460 return(_lwkt_trytokref(ref, td));
464 * Release a serializing token.
466 * WARNING! All tokens must be released in reverse order. This will be
470 lwkt_reltoken(lwkt_token_t tok)
472 thread_t td = curthread;
476 * Remove ref from thread token list and assert that it matches
477 * the token passed in. Tokens must be released in reverse order.
479 ref = td->td_toks_stop - 1;
480 KKASSERT(ref >= &td->td_toks_base && ref->tr_tok == tok);
481 td->td_toks_stop = ref;
484 * If the token was not MPSAFE release the MP lock.
486 if ((ref->tr_flags & LWKT_TOKEN_MPSAFE) == 0)
490 * Make sure the compiler does not reorder the clearing of
496 * Only clear the token if it matches ref. If ref was a recursively
497 * acquired token it may not match.
499 if (tok->t_ref == ref)
504 * Pool tokens are used to provide a type-stable serializing token
505 * pointer that does not race against disappearing data structures.
507 * This routine is called in early boot just after we setup the BSP's
508 * globaldata structure.
511 lwkt_token_pool_init(void)
515 for (i = 0; i < LWKT_NUM_POOL_TOKENS; ++i)
516 lwkt_token_init(&pool_tokens[i], 1, "pool");
520 lwkt_token_pool_lookup(void *ptr)
522 return (_lwkt_token_pool_lookup(ptr));
526 * Initialize a token. If mpsafe is 0, the MP lock is acquired before
527 * acquiring the token and released after releasing the token.
530 lwkt_token_init(lwkt_token_t tok, int mpsafe, const char *desc)
533 tok->t_flags = mpsafe ? LWKT_TOKEN_MPSAFE : 0;
534 tok->t_collisions = 0;
538 lwkt_token_uninit(lwkt_token_t tok)
545 lwkt_token_is_stale(lwkt_tokref_t ref)
547 lwkt_token_t tok = ref->tr_tok;
549 KKASSERT(tok->t_owner == curthread && ref->tr_state == 1 &&
552 /* Token is not stale */
553 if (tok->t_lastowner == tok->t_owner)
557 * The token is stale. Reset to not stale so that the next call to
558 * lwkt_token_is_stale will return "not stale" unless the token
559 * was acquired in-between by another thread.
561 tok->t_lastowner = tok->t_owner;