ACPI / EC: Fix race condition in ec_transaction_completed()

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>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 17 insertions, 13 deletions

diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index d016ea31b8e9..49d89909b4ed 100644
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -158,16 +158,17 @@ static int ec_transaction_completed(struct acpi_ec *ec)
         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 acpi_ec *ec)
                 } 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_handle gpe_device,
         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;
 }