[PATCH -v2] acpi: Fix possible recursive locking in hwregs.c

[Rakib Mullick <rakib.mullick@gmail.com>]

Calling pm-suspend might trigger a recursive lock in it's code path. In function acpi_hw_clear_acpi_status, acpi_os_acquire_lock holds the lock acpi_gbl_hardware_lock before calling acpi_hw_register_write(), then without releasing acpi_gbl_hardware_lock, this function calls acpi_ev_walk_gpe_list, which tries to hold acpi_gbl_gpe_lock. Both acpi_gbl_hardware_lock and acpi_gbl_gpe_lock are at same lock-class and which might cause lock recursion deadlock. 

Following patch fixes this scenario by just releasing acpi_gbl_hardware_lock before calling acpi_ev_walk_gpe_list.

 Changes since v0(https://lkml.org/lkml/2011/9/21/355):
	- Fix changelog, thanks to Lin Ming.

 Changes since v1 (https://lkml.org/lkml/2011/11/3/89):
	- Update changelog and rename goto label, courtesy Srivatsa S. Bhat.

Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
Cc: Lin Ming <ming.m.lin@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Len Brown <len.brown@intel.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

diff --git a/drivers/acpi/acpica/hwregs.c b/drivers/acpi/acpica/hwregs.c
index 55accb7..cc70f3f 100644
--- a/drivers/acpi/acpica/hwregs.c
+++ b/drivers/acpi/acpica/hwregs.c
@@ -269,16 +269,17 @@ acpi_status acpi_hw_clear_acpi_status(void)
 
 	status = acpi_hw_register_write(ACPI_REGISTER_PM1_STATUS,
 					ACPI_BITMASK_ALL_FIXED_STATUS);
-	if (ACPI_FAILURE(status)) {
-		goto unlock_and_exit;
-	}
+
+	acpi_os_release_lock(acpi_gbl_hardware_lock, lock_flags);
+
+	if (ACPI_FAILURE(status))
+		goto exit;
 
 	/* Clear the GPE Bits in all GPE registers in all GPE blocks */
 
 	status = acpi_ev_walk_gpe_list(acpi_hw_clear_gpe_block, NULL);
 
-      unlock_and_exit:
-	acpi_os_release_lock(acpi_gbl_hardware_lock, lock_flags);
+exit:
 	return_ACPI_STATUS(status);
 }