AcpiAcquireGlobalLock() can sometimes sleep if the mutex is contested.

The global lock is a memory region shared with the BIOS and thus
has some strange behavior like the fact that the sleep is 1 ms max.
We use standard mutexes to synchronize with the SCI so acquiring
the global lock after locking the mutex resulted in a witness
warning.

To deal with this for now, acquire the global lock before all other
locks, similar to Giant.  This should fix the witness "sleeping
with mutex held" issue on boot that occurred after the last ACPI-CA
import.  In the future, we hope to move to the new mutex interface
in ACPI-CA instead of the pseudo-semaphore version we have now.

Reviewed by:    jkim

1 files changed, 10 insertions, 13 deletions

diff --git a/sys/dev/acpica/acpi_ec.c b/sys/dev/acpica/acpi_ec.c
index 350fc86..2ba7958 100644
--- a/sys/dev/acpica/acpi_ec.c
+++ b/sys/dev/acpica/acpi_ec.c
@@ -312,37 +312,34 @@ EcLock(struct acpi_ec_softc *sc, int serialize)
 {
     ACPI_STATUS	status;
 
+    /* If _GLK is non-zero, acquire the global lock. */
+    status = AE_OK;
+    if (sc->ec_glk) {
+	status = AcpiAcquireGlobalLock(EC_LOCK_TIMEOUT, &sc->ec_glkhandle);
+	if (ACPI_FAILURE(status))
+	    return (status);
+    }
+
     /*
      * If caller is executing a series of commands, acquire the exclusive lock
      * to serialize with other users.
      * To sync with bottom-half interrupt handler, always acquire the mutex.
      */
-    status = AE_OK;
     if (serialize)
 	ACPI_SERIAL_BEGIN(ec);
     mtx_lock(&sc->ec_mtx);
 
-    /* If _GLK is non-zero, also acquire the global lock. */
-    if (sc->ec_glk) {
-	status = AcpiAcquireGlobalLock(EC_LOCK_TIMEOUT, &sc->ec_glkhandle);
-	if (ACPI_FAILURE(status)) {
-	    mtx_unlock(&sc->ec_mtx);
-	    if (serialize)
-		ACPI_SERIAL_END(ec);
-	}
-    }
-
     return (status);
 }
 
 static __inline void
 EcUnlock(struct acpi_ec_softc *sc)
 {
-    if (sc->ec_glk)
-	AcpiReleaseGlobalLock(sc->ec_glkhandle);
     mtx_unlock(&sc->ec_mtx);
     if (sx_xlocked(&ec_sxlock))
 	ACPI_SERIAL_END(ec);
+    if (sc->ec_glk)
+	AcpiReleaseGlobalLock(sc->ec_glkhandle);
 }
 
 static uint32_t		EcGpeHandler(void *Context);