ACPI / EC: Work around method reentrancy limit in ACPICA for _Qxx

A regression is caused by the following commit:

  Commit: 02b771b64b73226052d6e731a0987db3b47281e9
  Subject: ACPI / EC: Fix an issue caused by the serialized _Qxx evaluations

In this commit, using system workqueue causes that the maximum parallel
executions of _Qxx can exceed 255. This violates the method reentrancy
limit in ACPICA and generates the following error log:

  ACPI Error: Method reached maximum reentrancy limit (255) (20150818/dsmethod-341)

This patch creates a seperate workqueue and limits the number of parallel
_Qxx evaluations down to a configurable value (can be tuned against number
of online CPUs).

Since EC events are handled after driver probe, we can create the workqueue
in acpi_ec_init().

Fixes: 02b771b64b73 (ACPI / EC: Fix an issue caused by the serialized _Qxx evaluations)
Link: https://bugzilla.kernel.org/show_bug.cgi?id=135691
Cc: 4.3+ <stable@vger.kernel.org> # 4.3+
Reported-and-tested-by: Helen Buus <ubuntu@hbuus.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index b1050a0..13d1b94 100644 (file)
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -101,6 +101,7 @@ enum ec_command {
 #define ACPI_EC_UDELAY_POLL    550     /* Wait 1ms for EC transaction polling */
 #define ACPI_EC_CLEAR_MAX      100     /* Maximum number of events to query
                                         * when trying to clear the EC */
+#define ACPI_EC_MAX_QUERIES    16      /* Maximum number of parallel queries */
 
 enum {
        EC_FLAGS_QUERY_PENDING,         /* Query is pending */
@@ -121,6 +122,10 @@ static unsigned int ec_delay __read_mostly = ACPI_EC_DELAY;
 module_param(ec_delay, uint, 0644);
 MODULE_PARM_DESC(ec_delay, "Timeout(ms) waited until an EC command completes");
 
+static unsigned int ec_max_queries __read_mostly = ACPI_EC_MAX_QUERIES;
+module_param(ec_max_queries, uint, 0644);
+MODULE_PARM_DESC(ec_max_queries, "Maximum parallel _Qxx evaluations");
+
 static bool ec_busy_polling __read_mostly;
 module_param(ec_busy_polling, bool, 0644);
 MODULE_PARM_DESC(ec_busy_polling, "Use busy polling to advance EC transaction");
@@ -174,6 +179,7 @@ static void acpi_ec_event_processor(struct work_struct *work);
 
 struct acpi_ec *boot_ec, *first_ec;
 EXPORT_SYMBOL(first_ec);
+static struct workqueue_struct *ec_query_wq;
 
 static int EC_FLAGS_CLEAR_ON_RESUME; /* Needs acpi_ec_clear() on boot/resume */
 static int EC_FLAGS_QUERY_HANDSHAKE; /* Needs QR_EC issued when SCI_EVT set */
@@ -1098,7 +1104,7 @@ static int acpi_ec_query(struct acpi_ec *ec, u8 *data)
         * work queue execution.
         */
        ec_dbg_evt("Query(0x%02x) scheduled", value);
-       if (!schedule_work(&q->work)) {
+       if (!queue_work(ec_query_wq, &q->work)) {
                ec_dbg_evt("Query(0x%02x) overlapped", value);
                result = -EBUSY;
        }
@@ -1649,15 +1655,41 @@ static struct acpi_driver acpi_ec_driver = {
                },
 };
 
+static inline int acpi_ec_query_init(void)
+{
+       if (!ec_query_wq) {
+               ec_query_wq = alloc_workqueue("kec_query", 0,
+                                             ec_max_queries);
+               if (!ec_query_wq)
+                       return -ENODEV;
+       }
+       return 0;
+}
+
+static inline void acpi_ec_query_exit(void)
+{
+       if (ec_query_wq) {
+               destroy_workqueue(ec_query_wq);
+               ec_query_wq = NULL;
+       }
+}
+
 int __init acpi_ec_init(void)
 {
-       int result = 0;
+       int result;
 
+       /* register workqueue for _Qxx evaluations */
+       result = acpi_ec_query_init();
+       if (result)
+               goto err_exit;
        /* Now register the driver for the EC */
        result = acpi_bus_register_driver(&acpi_ec_driver);
-       if (result < 0)
-               return -ENODEV;
+       if (result)
+               goto err_exit;
 
+err_exit:
+       if (result)
+               acpi_ec_query_exit();
        return result;
 }
 
@@ -1667,5 +1699,6 @@ static void __exit acpi_ec_exit(void)
 {
 
        acpi_bus_unregister_driver(&acpi_ec_driver);
+       acpi_ec_query_exit();
 }
 #endif /* 0 */