Blame view
lib/rwsem.c
6.45 KB
1da177e4c Linux-2.6.12-rc2 |
1 2 3 4 5 6 7 8 9 |
/* rwsem.c: R/W semaphores: contention handling functions * * Written by David Howells (dhowells@redhat.com). * Derived from arch/i386/kernel/semaphore.c */ #include <linux/rwsem.h> #include <linux/sched.h> #include <linux/init.h> #include <linux/module.h> |
4ea2176df [PATCH] lockdep: ... |
10 11 12 13 14 15 16 17 18 19 20 |
/* * Initialize an rwsem: */ void __init_rwsem(struct rw_semaphore *sem, const char *name, struct lock_class_key *key) { #ifdef CONFIG_DEBUG_LOCK_ALLOC /* * Make sure we are not reinitializing a held semaphore: */ debug_check_no_locks_freed((void *)sem, sizeof(*sem)); |
4dfbb9d8c Lockdep: add lock... |
21 |
lockdep_init_map(&sem->dep_map, name, key, 0); |
4ea2176df [PATCH] lockdep: ... |
22 23 24 25 26 27 28 |
#endif sem->count = RWSEM_UNLOCKED_VALUE; spin_lock_init(&sem->wait_lock); INIT_LIST_HEAD(&sem->wait_list); } EXPORT_SYMBOL(__init_rwsem); |
1da177e4c Linux-2.6.12-rc2 |
29 30 31 32 33 34 35 |
struct rwsem_waiter { struct list_head list; struct task_struct *task; unsigned int flags; #define RWSEM_WAITING_FOR_READ 0x00000001 #define RWSEM_WAITING_FOR_WRITE 0x00000002 }; |
1da177e4c Linux-2.6.12-rc2 |
36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 |
/* * handle the lock release when processes blocked on it that can now run * - if we come here from up_xxxx(), then: * - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed) * - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so) * - there must be someone on the queue * - the spinlock must be held by the caller * - woken process blocks are discarded from the list after having task zeroed * - writers are only woken if downgrading is false */ static inline struct rw_semaphore * __rwsem_do_wake(struct rw_semaphore *sem, int downgrading) { struct rwsem_waiter *waiter; struct task_struct *tsk; struct list_head *next; signed long oldcount, woken, loop; |
1da177e4c Linux-2.6.12-rc2 |
53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 |
if (downgrading) goto dont_wake_writers; /* if we came through an up_xxxx() call, we only only wake someone up * if we can transition the active part of the count from 0 -> 1 */ try_again: oldcount = rwsem_atomic_update(RWSEM_ACTIVE_BIAS, sem) - RWSEM_ACTIVE_BIAS; if (oldcount & RWSEM_ACTIVE_MASK) goto undo; waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); /* try to grant a single write lock if there's a writer at the front * of the queue - note we leave the 'active part' of the count * incremented by 1 and the waiting part incremented by 0x00010000 */ if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE)) goto readers_only; /* We must be careful not to touch 'waiter' after we set ->task = NULL. * It is an allocated on the waiter's stack and may become invalid at * any time after that point (due to a wakeup from another source). */ list_del(&waiter->list); tsk = waiter->task; |
d59dd4620 [PATCH] use smp_m... |
80 |
smp_mb(); |
1da177e4c Linux-2.6.12-rc2 |
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 |
waiter->task = NULL; wake_up_process(tsk); put_task_struct(tsk); goto out; /* don't want to wake any writers */ dont_wake_writers: waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); if (waiter->flags & RWSEM_WAITING_FOR_WRITE) goto out; /* grant an infinite number of read locks to the readers at the front * of the queue * - note we increment the 'active part' of the count by the number of * readers before waking any processes up */ readers_only: woken = 0; do { woken++; if (waiter->list.next == &sem->wait_list) break; waiter = list_entry(waiter->list.next, struct rwsem_waiter, list); } while (waiter->flags & RWSEM_WAITING_FOR_READ); loop = woken; woken *= RWSEM_ACTIVE_BIAS - RWSEM_WAITING_BIAS; if (!downgrading) /* we'd already done one increment earlier */ woken -= RWSEM_ACTIVE_BIAS; rwsem_atomic_add(woken, sem); next = sem->wait_list.next; for (; loop > 0; loop--) { waiter = list_entry(next, struct rwsem_waiter, list); next = waiter->list.next; tsk = waiter->task; |
d59dd4620 [PATCH] use smp_m... |
123 |
smp_mb(); |
1da177e4c Linux-2.6.12-rc2 |
124 125 126 127 128 129 130 131 132 |
waiter->task = NULL; wake_up_process(tsk); put_task_struct(tsk); } sem->wait_list.next = next; next->prev = &sem->wait_list; out: |
1da177e4c Linux-2.6.12-rc2 |
133 134 135 136 137 138 139 140 141 142 143 144 |
return sem; /* undo the change to count, but check for a transition 1->0 */ undo: if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS, sem) != 0) goto out; goto try_again; } /* * wait for a lock to be granted */ |
c7af77b58 sched: mark rwsem... |
145 |
static struct rw_semaphore __sched * |
1da177e4c Linux-2.6.12-rc2 |
146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 |
rwsem_down_failed_common(struct rw_semaphore *sem, struct rwsem_waiter *waiter, signed long adjustment) { struct task_struct *tsk = current; signed long count; set_task_state(tsk, TASK_UNINTERRUPTIBLE); /* set up my own style of waitqueue */ spin_lock_irq(&sem->wait_lock); waiter->task = tsk; get_task_struct(tsk); list_add_tail(&waiter->list, &sem->wait_list); /* we're now waiting on the lock, but no longer actively read-locking */ count = rwsem_atomic_update(adjustment, sem); /* if there are no active locks, wake the front queued process(es) up */ if (!(count & RWSEM_ACTIVE_MASK)) sem = __rwsem_do_wake(sem, 0); spin_unlock_irq(&sem->wait_lock); /* wait to be given the lock */ for (;;) { if (!waiter->task) break; schedule(); set_task_state(tsk, TASK_UNINTERRUPTIBLE); } tsk->state = TASK_RUNNING; return sem; } /* * wait for the read lock to be granted */ |
d50efc6c4 x86: fix UML and ... |
186 |
asmregparm struct rw_semaphore __sched * |
1da177e4c Linux-2.6.12-rc2 |
187 188 189 |
rwsem_down_read_failed(struct rw_semaphore *sem) { struct rwsem_waiter waiter; |
1da177e4c Linux-2.6.12-rc2 |
190 191 192 |
waiter.flags = RWSEM_WAITING_FOR_READ; rwsem_down_failed_common(sem, &waiter, RWSEM_WAITING_BIAS - RWSEM_ACTIVE_BIAS); |
1da177e4c Linux-2.6.12-rc2 |
193 194 195 196 197 198 |
return sem; } /* * wait for the write lock to be granted */ |
d50efc6c4 x86: fix UML and ... |
199 |
asmregparm struct rw_semaphore __sched * |
1da177e4c Linux-2.6.12-rc2 |
200 201 202 |
rwsem_down_write_failed(struct rw_semaphore *sem) { struct rwsem_waiter waiter; |
1da177e4c Linux-2.6.12-rc2 |
203 204 |
waiter.flags = RWSEM_WAITING_FOR_WRITE; rwsem_down_failed_common(sem, &waiter, -RWSEM_ACTIVE_BIAS); |
1da177e4c Linux-2.6.12-rc2 |
205 206 207 208 209 210 211 |
return sem; } /* * handle waking up a waiter on the semaphore * - up_read/up_write has decremented the active part of count if we come here */ |
d50efc6c4 x86: fix UML and ... |
212 |
asmregparm struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem) |
1da177e4c Linux-2.6.12-rc2 |
213 214 |
{ unsigned long flags; |
1da177e4c Linux-2.6.12-rc2 |
215 216 217 218 219 220 221 |
spin_lock_irqsave(&sem->wait_lock, flags); /* do nothing if list empty */ if (!list_empty(&sem->wait_list)) sem = __rwsem_do_wake(sem, 0); spin_unlock_irqrestore(&sem->wait_lock, flags); |
1da177e4c Linux-2.6.12-rc2 |
222 223 224 225 226 227 228 229 |
return sem; } /* * downgrade a write lock into a read lock * - caller incremented waiting part of count and discovered it still negative * - just wake up any readers at the front of the queue */ |
d50efc6c4 x86: fix UML and ... |
230 |
asmregparm struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem) |
1da177e4c Linux-2.6.12-rc2 |
231 232 |
{ unsigned long flags; |
1da177e4c Linux-2.6.12-rc2 |
233 234 235 236 237 238 239 |
spin_lock_irqsave(&sem->wait_lock, flags); /* do nothing if list empty */ if (!list_empty(&sem->wait_list)) sem = __rwsem_do_wake(sem, 1); spin_unlock_irqrestore(&sem->wait_lock, flags); |
1da177e4c Linux-2.6.12-rc2 |
240 241 242 243 244 245 246 |
return sem; } EXPORT_SYMBOL(rwsem_down_read_failed); EXPORT_SYMBOL(rwsem_down_write_failed); EXPORT_SYMBOL(rwsem_wake); EXPORT_SYMBOL(rwsem_downgrade_wake); |