[PATCH 04/14] ACPI: Fix possible recursive locking in hwregs.c

[Len Brown <lenb@kernel.org>]

From: 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>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>
---
 drivers/acpi/acpica/hwregs.c |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

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);
 }
 
-- 
1.7.7.rc0.72.g4b5ea