X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=urcu.c;h=bf2a66bfe3ec360613497d6a7b7c0da2cddc10e9;hb=refs%2Fheads%2Fstable-0.8;hp=8cccbbce0868b518f9020f2d94eaedd41e22d2dc;hpb=f2aa49059a94eefed3bd9fbbbdd5207845c7ef39;p=userspace-rcu.git diff --git a/urcu.c b/urcu.c index 8cccbbc..bf2a66b 100644 --- a/urcu.c +++ b/urcu.c @@ -26,6 +26,7 @@ #define _BSD_SOURCE #define _GNU_SOURCE #define _LGPL_SOURCE +#define _DEFAULT_SOURCE #include #include #include @@ -63,18 +64,10 @@ #define RCU_QS_ACTIVE_ATTEMPTS 100 /* - * RCU_MEMBARRIER is only possibly available on Linux. + * The ABI of sys_membarrier changed after its original implementation. + * Disable it for now. Use RCU_MB flavor instead. */ -#if defined(RCU_MEMBARRIER) && defined(__linux__) -#include -#endif - -/* If the headers do not support SYS_membarrier, fall back on RCU_MB */ -#ifdef SYS_membarrier -# define membarrier(...) syscall(SYS_membarrier, __VA_ARGS__) -#else -# define membarrier(...) -ENOSYS -#endif +#define membarrier(...) -ENOSYS #define MEMBARRIER_EXPEDITED (1 << 0) #define MEMBARRIER_DELAYED (1 << 1) @@ -100,7 +93,21 @@ void __attribute__((constructor)) rcu_init(void); void __attribute__((destructor)) rcu_exit(void); #endif +/* + * rcu_gp_lock ensures mutual exclusion between threads calling + * synchronize_rcu(). + */ static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; +/* + * rcu_registry_lock ensures mutual exclusion between threads + * registering and unregistering themselves to/from the registry, and + * with threads reading that registry from synchronize_rcu(). However, + * this lock is not held all the way through the completion of awaiting + * for the grace period. It is sporadically released between iterations + * on the registry. + * rcu_registry_lock may nest inside rcu_gp_lock. + */ +static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER; struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT }; /* @@ -216,16 +223,46 @@ static void smp_mb_master(int group) /* * synchronize_rcu() waiting. Single thread. + * Always called with rcu_registry lock held. Releases this lock and + * grabs it again. Holds the lock when it returns. */ static void wait_gp(void) { - /* Read reader_gp before read futex */ + /* + * Read reader_gp before read futex. smp_mb_master() needs to + * be called with the rcu registry lock held in RCU_SIGNAL + * flavor. + */ smp_mb_master(RCU_MB_GROUP); - if (uatomic_read(&rcu_gp.futex) == -1) - futex_async(&rcu_gp.futex, FUTEX_WAIT, -1, - NULL, NULL, 0); + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); + if (uatomic_read(&rcu_gp.futex) != -1) + goto end; + while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1, + NULL, NULL, 0)) { + switch (errno) { + case EWOULDBLOCK: + /* Value already changed. */ + goto end; + case EINTR: + /* Retry if interrupted by signal. */ + break; /* Get out of switch. */ + default: + /* Unexpected error. */ + urcu_die(errno); + } + } +end: + /* + * Re-lock the registry lock before the next loop. + */ + mutex_lock(&rcu_registry_lock); } +/* + * Always called with rcu_registry lock held. Releases this lock between + * iterations and grabs it again. Holds the lock when it returns. + */ static void wait_for_readers(struct cds_list_head *input_readers, struct cds_list_head *cur_snap_readers, struct cds_list_head *qsreaders) @@ -282,10 +319,19 @@ static void wait_for_readers(struct cds_list_head *input_readers, } break; } else { - if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) + if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + /* wait_gp unlocks/locks registry lock. */ wait_gp(); - else + } else { + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); caa_cpu_relax(); + /* + * Re-lock the registry lock before the + * next loop. + */ + mutex_lock(&rcu_registry_lock); + } } #else /* #ifndef HAS_INCOHERENT_CACHES */ /* @@ -306,10 +352,18 @@ static void wait_for_readers(struct cds_list_head *input_readers, wait_gp_loops = 0; } if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { + /* wait_gp unlocks/locks registry lock. */ wait_gp(); wait_gp_loops++; } else { + /* Temporarily unlock the registry lock. */ + mutex_unlock(&rcu_registry_lock); caa_cpu_relax(); + /* + * Re-lock the registry lock before the + * next loop. + */ + mutex_lock(&rcu_registry_lock); } } #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ @@ -348,17 +402,23 @@ void synchronize_rcu(void) */ urcu_move_waiters(&waiters, &gp_waiters); + mutex_lock(&rcu_registry_lock); + if (cds_list_empty(®istry)) goto out; - /* All threads should read qparity before accessing data structure - * where new ptr points to. Must be done within rcu_gp_lock because it - * iterates on reader threads.*/ + /* + * All threads should read qparity before accessing data structure + * where new ptr points to. Must be done within rcu_registry_lock + * because it iterates on reader threads. + */ /* Write new ptr before changing the qparity */ smp_mb_master(RCU_MB_GROUP); /* * Wait for readers to observe original parity or be quiescent. + * wait_for_readers() can release and grab again rcu_registry_lock + * interally. */ wait_for_readers(®istry, &cur_snap_readers, &qsreaders); @@ -399,6 +459,8 @@ void synchronize_rcu(void) /* * Wait for readers to observe new parity or be quiescent. + * wait_for_readers() can release and grab again rcu_registry_lock + * interally. */ wait_for_readers(&cur_snap_readers, NULL, &qsreaders); @@ -407,11 +469,14 @@ void synchronize_rcu(void) */ cds_list_splice(&qsreaders, ®istry); - /* Finish waiting for reader threads before letting the old ptr being - * freed. Must be done within rcu_gp_lock because it iterates on reader - * threads. */ + /* + * Finish waiting for reader threads before letting the old ptr + * being freed. Must be done within rcu_registry_lock because it + * iterates on reader threads. + */ smp_mb_master(RCU_MB_GROUP); out: + mutex_unlock(&rcu_registry_lock); mutex_unlock(&rcu_gp_lock); /* @@ -447,17 +512,17 @@ void rcu_register_thread(void) assert(URCU_TLS(rcu_reader).need_mb == 0); assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK)); - mutex_lock(&rcu_gp_lock); + mutex_lock(&rcu_registry_lock); rcu_init(); /* In case gcc does not support constructor attribute */ cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); - mutex_unlock(&rcu_gp_lock); + mutex_unlock(&rcu_registry_lock); } void rcu_unregister_thread(void) { - mutex_lock(&rcu_gp_lock); + mutex_lock(&rcu_registry_lock); cds_list_del(&URCU_TLS(rcu_reader).node); - mutex_unlock(&rcu_gp_lock); + mutex_unlock(&rcu_registry_lock); } #ifdef RCU_MEMBARRIER @@ -488,9 +553,9 @@ static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context) * rcu_init constructor. Called when the library is linked, but also when * reader threads are calling rcu_register_thread(). * Should only be called by a single thread at a given time. This is ensured by - * holing the rcu_gp_lock from rcu_register_thread() or by running at library - * load time, which should not be executed by multiple threads nor concurrently - * with rcu_register_thread() anyway. + * holing the rcu_registry_lock from rcu_register_thread() or by running + * at library load time, which should not be executed by multiple + * threads nor concurrently with rcu_register_thread() anyway. */ void rcu_init(void) {