Index: uspace/lib/libc/generic/futex.c =================================================================== --- uspace/lib/libc/generic/futex.c (revision b3c38750a1d4b8fe19c67acaa51288310cd9ba5d) +++ uspace/lib/libc/generic/futex.c (revision 4db6eaf06a371efbb5d1f20919cbf3e224a20036) @@ -1,4 +1,4 @@ /* - * Copyright (c) 2006 Jakub Jermar + * Copyright (c) 2008 Jakub Jermar * All rights reserved. * @@ -42,6 +42,6 @@ /* * Note about race conditions. - * Because of non-atomic nature of operations performed sequentially on the futex - * counter and the futex wait queue, there is a race condition: + * Because of non-atomic nature of operations performed sequentially on the + * futex counter and the futex wait queue, there is a race condition: * * (wq->missed_wakeups == 1) && (futex->count = 1) @@ -55,69 +55,81 @@ * 5. B has to call SYS_FUTEX_WAKEUP syscall to wake up the sleeping thread * 6. B finds the wait queue empty and changes wq->missed_wakeups from 0 to 1 - * 7. A fixes futex->count (i.e. the number of waiting threads) by changing it from 0 to 1 + * 7. A fixes futex->count (i.e. the number of waiting threads) by changing it + * from 0 to 1 * * Scenario 2 (conditional down operation vs. futex_up) * 1. assume wq->missed_wakeups == 0 && futex->count == 0 * (i.e. thread A is in the critical section) - * 2. thread B performs futex_trydown() operation and changes futex->count from 0 to -1 + * 2. thread B performs futex_trydown() operation and changes futex->count from + * 0 to -1 * B is now obliged to call SYS_FUTEX_SLEEP syscall * 3. A wants to leave the critical section and does futex_up() - * 4. A thus changes futex->count from -1 to 0 and must call SYS_FUTEX_WAKEUP syscall + * 4. A thus changes futex->count from -1 to 0 and must call SYS_FUTEX_WAKEUP + * syscall * 5. B finds the wait queue empty and immediatelly aborts the conditional sleep - * 6. No thread is queueing in the wait queue so wq->missed_wakeups changes from 0 to 1 - * 6. B fixes futex->count (i.e. the number of waiting threads) by changing it from 0 to 1 + * 6. No thread is queueing in the wait queue so wq->missed_wakeups changes from + * 0 to 1 + * 6. B fixes futex->count (i.e. the number of waiting threads) by changing it + * from 0 to 1 * - * Both scenarios allow two threads to be in the critical section simultaneously. - * One without kernel intervention and the other through wq->missed_wakeups being 1. + * Both scenarios allow two threads to be in the critical section + * simultaneously. One without kernel intervention and the other through + * wq->missed_wakeups being 1. * - * To mitigate this problem, futex_down_timeout() detects that the syscall didn't sleep - * in the wait queue, fixes the futex counter and RETRIES the whole operation again. - * + * To mitigate this problem, futex_down_timeout() detects that the syscall + * didn't sleep in the wait queue, fixes the futex counter and RETRIES the + * whole operation again. */ /** Initialize futex counter. * - * @param futex Futex. - * @param val Initialization value. + * @param futex Futex. + * @param val Initialization value. */ -void futex_initialize(atomic_t *futex, int val) +void futex_initialize(futex_t *futex, int val) { atomic_set(futex, val); } -int futex_down(atomic_t *futex) +int futex_down(futex_t *futex) { return futex_down_timeout(futex, SYNCH_NO_TIMEOUT, SYNCH_FLAGS_NONE); } -int futex_trydown(atomic_t *futex) +int futex_trydown(futex_t *futex) { - return futex_down_timeout(futex, SYNCH_NO_TIMEOUT, SYNCH_FLAGS_NON_BLOCKING); + return futex_down_timeout(futex, SYNCH_NO_TIMEOUT, + SYNCH_FLAGS_NON_BLOCKING); } /** Try to down the futex. * - * @param futex Futex. - * @param usec Microseconds to wait. Zero value means sleep without timeout. - * @param flags Select mode of operation. See comment for waitq_sleep_timeout(). + * @param futex Futex. + * @param usec Microseconds to wait. Zero value means sleep without + * timeout. + * @param flags Select mode of operation. See comment for + * waitq_sleep_timeout(). * - * @return ENOENT if there is no such virtual address. One of ESYNCH_OK_ATOMIC - * and ESYNCH_OK_BLOCKED on success or ESYNCH_TIMEOUT if the lock was - * not acquired because of a timeout or ESYNCH_WOULD_BLOCK if the - * operation could not be carried out atomically (if requested so). + * @return ENOENT if there is no such virtual address. One of + * ESYNCH_OK_ATOMIC and ESYNCH_OK_BLOCKED on success or + * ESYNCH_TIMEOUT if the lock was not acquired because of + * a timeout or ESYNCH_WOULD_BLOCK if the operation could + * not be carried out atomically (if requested so). */ -int futex_down_timeout(atomic_t *futex, uint32_t usec, int flags) +int futex_down_timeout(futex_t *futex, uint32_t usec, int flags) { int rc; while (atomic_predec(futex) < 0) { - rc = __SYSCALL3(SYS_FUTEX_SLEEP, (sysarg_t) &futex->count, (sysarg_t) usec, (sysarg_t) flags); + rc = __SYSCALL3(SYS_FUTEX_SLEEP, (sysarg_t) &futex->count, + (sysarg_t) usec, (sysarg_t) flags); switch (rc) { case ESYNCH_OK_ATOMIC: /* - * Because of a race condition between timeout and futex_up() - * and between conditional futex_down_timeout() and futex_up(), - * we have to give up and try again in this special case. + * Because of a race condition between timeout and + * futex_up() and between conditional + * futex_down_timeout() and futex_up(), we have to give + * up and try again in this special case. */ atomic_inc(futex); @@ -131,7 +143,8 @@ case ESYNCH_WOULD_BLOCK: /* - * The conditional down operation should be implemented this way. - * The userspace-only variant tends to accumulate missed wakeups - * in the kernel futex wait queue. + * The conditional down operation should be implemented + * this way. The userspace-only variant tends to + * accumulate missed wakeups in the kernel futex wait + * queue. */ atomic_inc(futex); @@ -142,5 +155,6 @@ /* * Enter the critical section. - * The futex counter has already been incremented for us. + * The futex counter has already been incremented for + * us. */ return ESYNCH_OK_BLOCKED; @@ -159,9 +173,10 @@ /** Up the futex. * - * @param futex Futex. + * @param futex Futex. * - * @return ENOENT if there is no such virtual address. Otherwise zero. + * @return ENOENT if there is no such virtual address. Otherwise + * zero. */ -int futex_up(atomic_t *futex) +int futex_up(futex_t *futex) { long val; Index: uspace/lib/libc/include/futex.h =================================================================== --- uspace/lib/libc/include/futex.h (revision b3c38750a1d4b8fe19c67acaa51288310cd9ba5d) +++ uspace/lib/libc/include/futex.h (revision 4db6eaf06a371efbb5d1f20919cbf3e224a20036) @@ -41,9 +41,11 @@ #define FUTEX_INITIALIZER {1} -extern void futex_initialize(atomic_t *futex, int value); -extern int futex_down(atomic_t *futex); -extern int futex_trydown(atomic_t *futex); -extern int futex_down_timeout(atomic_t *futex, uint32_t usec, int flags); -extern int futex_up(atomic_t *futex); +typedef atomic_t futex_t; + +extern void futex_initialize(futex_t *futex, int value); +extern int futex_down(futex_t *futex); +extern int futex_trydown(futex_t *futex); +extern int futex_down_timeout(futex_t *futex, uint32_t usec, int flags); +extern int futex_up(futex_t *futex); #endif Index: uspace/srv/vfs/vfs.h =================================================================== --- uspace/srv/vfs/vfs.h (revision b3c38750a1d4b8fe19c67acaa51288310cd9ba5d) +++ uspace/srv/vfs/vfs.h (revision 4db6eaf06a371efbb5d1f20919cbf3e224a20036) @@ -1,4 +1,4 @@ /* - * Copyright (c) 2007 Jakub Jermar + * Copyright (c) 2008 Jakub Jermar * All rights reserved. * @@ -137,6 +137,8 @@ link_t nh_link; /**< Node hash-table link. */ - /** Holding this rwlock prevents modifications of the node's contents. */ - atomic_t contents_rwlock; + /** + * Holding this rwlock prevents modifications of the node's contents. + */ + rwlock_t contents_rwlock; } vfs_node_t;