From 044c73a55dbc3223cc02c10e11fc7798bf41a242 Mon Sep 17 00:00:00 2001 From: Rickard Green Date: Thu, 19 Aug 2010 18:57:03 +0200 Subject: Fix race in erts_poll() A race condition in erts_poll() could cause delay of poll for I/O. --- erts/emulator/sys/common/erl_poll.c | 39 +++++++++++++++++++------------------ 1 file changed, 20 insertions(+), 19 deletions(-) (limited to 'erts/emulator/sys') diff --git a/erts/emulator/sys/common/erl_poll.c b/erts/emulator/sys/common/erl_poll.c index 09fb6337f7..c17806d96c 100644 --- a/erts/emulator/sys/common/erl_poll.c +++ b/erts/emulator/sys/common/erl_poll.c @@ -286,7 +286,7 @@ struct ErtsPollSet_ { ErtsPollSet next; int internal_fd_limit; ErtsFdStatus *fds_status; - int no_of_user_fds; + erts_smp_atomic_t no_of_user_fds; int fds_status_len; #if ERTS_POLL_USE_KERNEL_POLL int kp_fd; @@ -852,7 +852,7 @@ write_batch_buf(ErtsPollSet ps, ErtsPollBatchBuf *bbp) ps->fds_status[fd].flags |= ERTS_POLL_FD_FLG_USEFLBCK; ASSERT(ps->fds_status[fd].used_events); ps->fds_status[fd].used_events = 0; - ps->no_of_user_fds--; + erts_smp_atomic_dec(&ps->no_of_user_fds); update_fallback_pollset(ps, fd); ASSERT(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK); break; @@ -902,11 +902,11 @@ batch_update_pollset(ErtsPollSet ps, int fd, ErtsPollBatchBuf *bbp) events = ERTS_POLL_EV_E2N(ps->fds_status[fd].events); if (!events) { buf[buf_len].events = POLLREMOVE; - ps->no_of_user_fds--; + erts_smp_atomic_dec(&ps->no_of_user_fds); } else if (!ps->fds_status[fd].used_events) { buf[buf_len].events = events; - ps->no_of_user_fds++; + erts_smp_atomic_inc(&ps->no_of_user_fds); } else { if ((ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_RST) @@ -996,12 +996,12 @@ batch_update_pollset(ErtsPollSet ps, int fd, ErtsPollBatchBuf *bbp) } if (used_events) { if (!events) { - ps->no_of_user_fds--; + erts_smp_atomic_dec(&ps->no_of_user_fds); } } else { if (events) - ps->no_of_user_fds++; + erts_smp_atomic_inc(&ps->no_of_user_fds); } ASSERT((events & ~(ERTS_POLL_EV_IN|ERTS_POLL_EV_OUT)) == 0); ASSERT((used_events & ~(ERTS_POLL_EV_IN|ERTS_POLL_EV_OUT)) == 0); @@ -1075,7 +1075,7 @@ update_pollset(ErtsPollSet ps, int fd) epe.data.fd = epe_templ.data.fd; res = epoll_ctl(ps->kp_fd, EPOLL_CTL_DEL, fd, &epe); } while (res != 0 && errno == EINTR); - ps->no_of_user_fds--; + erts_smp_atomic_dec(&ps->no_of_user_fds); ps->fds_status[fd].used_events = 0; } @@ -1083,11 +1083,11 @@ update_pollset(ErtsPollSet ps, int fd) /* A note on EPOLL_CTL_DEL: linux kernel versions before 2.6.9 need a non-NULL event pointer even though it is ignored... */ op = EPOLL_CTL_DEL; - ps->no_of_user_fds--; + erts_smp_atomic_dec(&ps->no_of_user_fds); } else if (!ps->fds_status[fd].used_events) { op = EPOLL_CTL_ADD; - ps->no_of_user_fds++; + erts_smp_atomic_inc(&ps->no_of_user_fds); } else { op = EPOLL_CTL_MOD; @@ -1137,7 +1137,7 @@ update_pollset(ErtsPollSet ps, int fd) /* Fall through ... */ case EPOLL_CTL_ADD: { ps->fds_status[fd].flags |= ERTS_POLL_FD_FLG_USEFLBCK; - ps->no_of_user_fds--; + erts_smp_atomic_dec(&ps->no_of_user_fds); #if ERTS_POLL_USE_CONCURRENT_UPDATE if (!*update_fallback) { *update_fallback = 1; @@ -1225,7 +1225,7 @@ static int update_pollset(ErtsPollSet ps, int fd) #if ERTS_POLL_USE_FALLBACK ASSERT(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK); #endif - ps->no_of_user_fds--; + erts_smp_atomic_dec(&ps->no_of_user_fds); last_pix = --ps->no_poll_fds; if (pix != last_pix) { /* Move last pix to this pix */ @@ -1252,7 +1252,7 @@ static int update_pollset(ErtsPollSet ps, int fd) ASSERT(!(ps->fds_status[fd].flags & ERTS_POLL_FD_FLG_INFLBCK) || fd == ps->kp_fd); #endif - ps->no_of_user_fds++; + erts_smp_atomic_inc(&ps->no_of_user_fds); ps->fds_status[fd].pix = pix = ps->no_poll_fds++; if (pix >= ps->poll_fds_len) grow_poll_fds(ps, pix); @@ -1303,7 +1303,7 @@ static int update_pollset(ErtsPollSet ps, int fd) if (!ps->fds_status[fd].used_events) { ASSERT(events); - ps->no_of_user_fds++; + erts_smp_atomic_inc(&ps->no_of_user_fds); #if ERTS_POLL_USE_FALLBACK ps->no_select_fds++; ps->fds_status[fd].flags |= ERTS_POLL_FD_FLG_INFLBCK; @@ -1311,7 +1311,7 @@ static int update_pollset(ErtsPollSet ps, int fd) } else if (!events) { ASSERT(ps->fds_status[fd].used_events); - ps->no_of_user_fds--; + erts_smp_atomic_dec(&ps->no_of_user_fds); ps->fds_status[fd].events = events; #if ERTS_POLL_USE_FALLBACK ps->no_select_fds--; @@ -1912,7 +1912,8 @@ static ERTS_INLINE int check_fd_events(ErtsPollSet ps, SysTimeval *tv, int max_res, int *ps_locked) { ASSERT(!*ps_locked); - if (ps->no_of_user_fds == 0 && tv->tv_usec == 0 && tv->tv_sec == 0) { + if (erts_smp_atomic_read(&ps->no_of_user_fds) == 0 + && tv->tv_usec == 0 && tv->tv_sec == 0) { /* Nothing to poll and zero timeout; done... */ return 0; } @@ -1950,7 +1951,7 @@ check_fd_events(ErtsPollSet ps, SysTimeval *tv, int max_res, int *ps_locked) * the maximum number of file descriptors in the poll set. */ struct dvpoll poll_res; - int nfds = ps->no_of_user_fds; + int nfds = (int) erts_smp_atomic_read(&ps->no_of_user_fds); #ifdef ERTS_SMP nfds++; /* Wakeup pipe */ #endif @@ -2228,7 +2229,7 @@ ERTS_POLL_EXPORT(erts_poll_create_pollset)(void) ps->internal_fd_limit = 0; ps->fds_status = NULL; ps->fds_status_len = 0; - ps->no_of_user_fds = 0; + erts_smp_atomic_init(&ps->no_of_user_fds, 0); #if ERTS_POLL_USE_KERNEL_POLL ps->kp_fd = -1; #if ERTS_POLL_USE_EPOLL @@ -2326,7 +2327,7 @@ ERTS_POLL_EXPORT(erts_poll_create_pollset)(void) #if ERTS_POLL_USE_FALLBACK ps->fallback_used = 0; #endif - ps->no_of_user_fds = 0; /* Don't count wakeup pipe and fallback fd */ + erts_smp_atomic_set(&ps->no_of_user_fds, 0); /* Don't count wakeup pipe and fallback fd */ erts_smp_spin_lock(&pollsets_lock); ps->next = pollsets; @@ -2472,7 +2473,7 @@ ERTS_POLL_EXPORT(erts_poll_info)(ErtsPollSet ps, ErtsPollInfo *pip) pip->memory_size = size; - pip->poll_set_size = ps->no_of_user_fds; + pip->poll_set_size = (int) erts_smp_atomic_read(&ps->no_of_user_fds); #ifdef ERTS_SMP pip->poll_set_size++; /* Wakeup pipe */ #endif -- cgit v1.2.3