From 33fea794b9deeb8ffb77e284eb37375b8f45a2c4 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Tue, 27 Jul 2010 19:29:38 +0200 Subject: [S390] etr: fix clock synchronization race The etr events switch-to-local and sync-check disable the synchronous clock and schedule a work queue that tries to get the clock back into sync. If another switch-to-local or sync-check event occurs while the work queue function etr_work_fn still runs the eacr.es bit and the clock_sync_word can become inconsistent because check_sync_clock only uses the clock_sync_word to determine if the clock is in sync or not. The second pass of the etr_work_fn will reset the eacr.es bit but will leave the clock_sync_word intact. Fix this race by moving the reset of the eacr.es bit into the switch-to-local and sync-check functions and by checking the eacr.es bit as well to decide if the clock needs to be synced. Signed-off-by: Martin Schwidefsky --- arch/s390/kernel/time.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) (limited to 'arch/s390') diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c index a2163c95eb9..15a7536452d 100644 --- a/arch/s390/kernel/time.c +++ b/arch/s390/kernel/time.c @@ -524,8 +524,11 @@ void etr_switch_to_local(void) if (!etr_eacr.sl) return; disable_sync_clock(NULL); - set_bit(ETR_EVENT_SWITCH_LOCAL, &etr_events); - queue_work(time_sync_wq, &etr_work); + if (!test_and_set_bit(ETR_EVENT_SWITCH_LOCAL, &etr_events)) { + etr_eacr.es = etr_eacr.sl = 0; + etr_setr(&etr_eacr); + queue_work(time_sync_wq, &etr_work); + } } /* @@ -539,8 +542,11 @@ void etr_sync_check(void) if (!etr_eacr.es) return; disable_sync_clock(NULL); - set_bit(ETR_EVENT_SYNC_CHECK, &etr_events); - queue_work(time_sync_wq, &etr_work); + if (!test_and_set_bit(ETR_EVENT_SYNC_CHECK, &etr_events)) { + etr_eacr.es = 0; + etr_setr(&etr_eacr); + queue_work(time_sync_wq, &etr_work); + } } /* @@ -902,7 +908,7 @@ static struct etr_eacr etr_handle_update(struct etr_aib *aib, * Do not try to get the alternate port aib if the clock * is not in sync yet. */ - if (!check_sync_clock()) + if (!eacr.es || !check_sync_clock()) return eacr; /* @@ -1064,7 +1070,7 @@ static void etr_work_fn(struct work_struct *work) * If the clock is in sync just update the eacr and return. * If there is no valid sync port wait for a port update. */ - if (check_sync_clock() || sync_port < 0) { + if ((eacr.es && check_sync_clock()) || sync_port < 0) { etr_update_eacr(eacr); etr_set_tolec_timeout(now); goto out_unlock; -- cgit v1.2.3