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ACPI / EC: Fix a race issue in acpi_ec_guard_event() 

In acpi_ec_guard_event(), EC transaction state machine variables should be
checked with the EC spinlock locked.
The bug doesn't trigger any real issue now because this bug can only occur
when the ec_event_clearing=event mode is applied while there is no user
currently using this mode.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Lv Zheng 2015-09-24 14:54:54 +08:00 committed by Rafael J. Wysocki
parent 0700c047f6
commit 6119754707
1 changed files with 29 additions and 13 deletions
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42
drivers/acpi/ec.c
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@ -441,17 +441,31 @@ static void acpi_ec_complete_query(struct acpi_ec *ec)
static bool acpi_ec_guard_event(struct acpi_ec *ec)
{
bool guarded = true;
unsigned long flags;
spin_lock_irqsave(&ec->lock, flags);
/*
* If firmware SCI_EVT clearing timing is "event", we actually
* don't know when the SCI_EVT will be cleared by firmware after
* evaluating _Qxx, so we need to re-check SCI_EVT after waiting an
* acceptable period.
*
* The guarding period begins when EC_FLAGS_QUERY_PENDING is
* flagged, which means SCI_EVT check has just been performed.
* But if the current transaction is ACPI_EC_COMMAND_QUERY, the
* guarding should have already been performed (via
* EC_FLAGS_QUERY_GUARDING) and should not be applied so that the
* ACPI_EC_COMMAND_QUERY transaction can be transitioned into
* ACPI_EC_COMMAND_POLL state immediately.
*/
if (ec_event_clearing == ACPI_EC_EVT_TIMING_STATUS ||
ec_event_clearing == ACPI_EC_EVT_TIMING_QUERY ||
!test_bit(EC_FLAGS_QUERY_PENDING, &ec->flags) ||
(ec->curr && ec->curr->command == ACPI_EC_COMMAND_QUERY))
return false;
/*
* Postpone the query submission to allow the firmware to proceed,
* we shouldn't check SCI_EVT before the firmware reflagging it.
*/
return true;
guarded = false;
spin_unlock_irqrestore(&ec->lock, flags);
return guarded;
}
static int ec_transaction_polled(struct acpi_ec *ec)
@ -597,6 +611,7 @@ static int ec_guard(struct acpi_ec *ec)
unsigned long guard = usecs_to_jiffies(ec_polling_guard);
unsigned long timeout = ec->timestamp + guard;
/* Ensure guarding period before polling EC status */
do {
if (ec_busy_polling) {
/* Perform busy polling */
@ -606,11 +621,13 @@ static int ec_guard(struct acpi_ec *ec)
} else {
/*
* Perform wait polling
*
* For SCI_EVT clearing timing of "event",
* performing guarding before re-checking the
* SCI_EVT. Otherwise, such guarding is not needed
* due to the old practices.
* 1. Wait the transaction to be completed by the
* GPE handler after the transaction enters
* ACPI_EC_COMMAND_POLL state.
* 2. A special guarding logic is also required
* for event clearing mode "event" before the
* transaction enters ACPI_EC_COMMAND_POLL
* state.
*/
if (!ec_transaction_polled(ec) &&
!acpi_ec_guard_event(ec))
@ -620,7 +637,6 @@ static int ec_guard(struct acpi_ec *ec)
guard))
return 0;
}
/* Guard the register accesses for the polling modes */
} while (time_before(jiffies, timeout));
return -ETIME;
}