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[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 <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2010-07-27 19:29:38 +02:00 committed by Martin Schwidefsky
parent f5cdac274c
commit 33fea794b9
1 changed files with 12 additions and 6 deletions
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14
arch/s390/kernel/time.c
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@ -524,9 +524,12 @@ void etr_switch_to_local(void)
if (!etr_eacr.sl)
return;
disable_sync_clock(NULL);
set_bit(ETR_EVENT_SWITCH_LOCAL, &etr_events);
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);
}
}
/*
* ETR sync check machine check. This is called when the ETR OTE and the
@ -539,9 +542,12 @@ void etr_sync_check(void)
if (!etr_eacr.es)
return;
disable_sync_clock(NULL);
set_bit(ETR_EVENT_SYNC_CHECK, &etr_events);
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);
}
}
/*
* ETR timing alert. There are two causes:
@ -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;