[PATCH 3.15 27/84] ACPI / EC: Fix race condition in ec_transaction_completed()

Greg Kroah-Hartman
2014-07-15T23:43:14Z

From: Lv Zheng <lv.zheng@intel.com>

commit c0d653412fc8450370167a3268b78fc772ff9c87 upstream.

There is a race condition in ec_transaction_completed().

When ec_transaction_completed() is called in the GPE handler, it could
return true because of (ec->curr == NULL). Then the wake_up() invocation
could complete the next command unexpectedly since there is no lock between
the 2 invocations. With the previous cleanup, the IBF=0 waiter race need
not be handled any more. It's now safe to return a flag from
advance_condition() to indicate the requirement of wakeup, the flag is
returned from a locked context.

The ec_transaction_completed() is now only invoked by the ec_poll() where
the ec->curr is ensured to be different from NULL.

After cleaning up, the EVT_SCI=1 check should be moved out of the wakeup
condition so that an EVT_SCI raised with (ec->curr == NULL) can trigger a
QR_SC command.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=70891
Link: https://bugzilla.kernel.org/show_bug.cgi?id=63931
Link: https://bugzilla.kernel.org/show_bug.cgi?id=59911
Reported-and-tested-by: Gareth Williams <gareth@garethwilliams.me.uk>
Reported-and-tested-by: Hans de Goede <jwrdegoede@fedoraproject.org>
Reported-by: Barton Xu <tank.xuhan@gmail.com>
Tested-by: Steffen Weber <steffen.weber@gmail.com>
Tested-by: Arthur Chen <axchen@nvidia.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/acpi/ec.c | 30 +++++++++++++++++-------------
1 file changed, 17 insertions(+), 13 deletions(-)

--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -158,16 +158,17 @@ static int ec_transaction_completed(stru
unsigned long flags;
int ret = 0;
spin_lock_irqsave(&ec->lock, flags);
- if (!ec->curr || (ec->curr->flags & ACPI_EC_COMMAND_COMPLETE))
+ if (ec->curr && (ec->curr->flags & ACPI_EC_COMMAND_COMPLETE))
ret = 1;
spin_unlock_irqrestore(&ec->lock, flags);
return ret;
}

-static void advance_transaction(struct acpi_ec *ec)
+static bool advance_transaction(struct acpi_ec *ec)
{
struct transaction *t;
u8 status;
+ bool wakeup = false;

pr_debug("===== %s =====\n", in_interrupt() ? "IRQ" : "TASK");
status = acpi_ec_read_status(ec);
@@ -183,21 +184,25 @@ static void advance_transaction(struct a
} else if (t->rlen > t->ri) {
if ((status & ACPI_EC_FLAG_OBF) == 1) {
t->rdata[t->ri++] = acpi_ec_read_data(ec);
- if (t->rlen == t->ri)
+ if (t->rlen == t->ri) {
t->flags |= ACPI_EC_COMMAND_COMPLETE;
+ wakeup = true;
+ }
} else
goto err;
} else if (t->wlen == t->wi &&
- (status & ACPI_EC_FLAG_IBF) == 0)
+ (status & ACPI_EC_FLAG_IBF) == 0) {
t->flags |= ACPI_EC_COMMAND_COMPLETE;
- return;
+ wakeup = true;
+ }
+ return wakeup;
} else {
if ((status & ACPI_EC_FLAG_IBF) == 0) {
acpi_ec_write_cmd(ec, t->command);
t->flags |= ACPI_EC_COMMAND_POLL;
} else
goto err;
- return;
+ return wakeup;
}
err:
/*
@@ -208,13 +213,14 @@ err:
if (in_interrupt() && t)
++t->irq_count;
}
+ return wakeup;
}

static void start_transaction(struct acpi_ec *ec)
{
ec->curr->irq_count = ec->curr->wi = ec->curr->ri = 0;
ec->curr->flags = 0;
- advance_transaction(ec);
+ (void)advance_transaction(ec);
}

static int acpi_ec_sync_query(struct acpi_ec *ec, u8 *data);
@@ -248,7 +254,7 @@ static int ec_poll(struct acpi_ec *ec)
return 0;
}
spin_lock_irqsave(&ec->lock, flags);
- advance_transaction(ec);
+ (void)advance_transaction(ec);
spin_unlock_irqrestore(&ec->lock, flags);
} while (time_before(jiffies, delay));
pr_debug("controller reset, restart transaction\n");
@@ -627,12 +633,10 @@ static u32 acpi_ec_gpe_handler(acpi_hand
struct acpi_ec *ec = data;

spin_lock_irqsave(&ec->lock, flags);
- advance_transaction(ec);
- spin_unlock_irqrestore(&ec->lock, flags);
- if (ec_transaction_completed(ec)) {
+ if (advance_transaction(ec))
wake_up(&ec->wait);
- ec_check_sci(ec, acpi_ec_read_status(ec));
- }
+ spin_unlock_irqrestore(&ec->lock, flags);
+ ec_check_sci(ec, acpi_ec_read_status(ec));
return ACPI_INTERRUPT_HANDLED | ACPI_REENABLE_GPE;
}