Commit 2140b66b authored by Pierre-Louis Bossart's avatar Pierre-Louis Bossart Committed by Vinod Koul
Browse files

soundwire: bus: fix race condition with probe_complete signaling 



The driver probe takes care of basic initialization and is invoked
when a Slave becomes attached, after a match between the Slave DevID
registers and ACPI/DT entries.

The update_status callback is invoked when a Slave state changes,
e.g. when it is assigned a non-zero Device Number and it reports with
an ATTACHED/ALERT state.

The state change detection is usually hardware-based and based on the
SoundWire frame rate (e.g. double-digit microseconds) while the probe
is a pure software operation, which may involve a kernel module
load. In corner cases, it's possible that the state changes before the
probe completes.

This patch suggests the use of wait_for_completion to avoid races on
startup, so that the update_status callback does not rely on invalid
pointers/data structures.

Signed-off-by: default avatarRander Wang <rander.wang@intel.com>
Signed-off-by: default avatarPierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200115000844.14695-2-pierre-louis.bossart@linux.intel.com


Signed-off-by: default avatarVinod Koul <vkoul@kernel.org>
parent eff346f2

drivers/soundwire/bus.c

+22 −3
Original line number Diff line number Diff line
@@ -970,10 +970,29 @@ static int sdw_handle_slave_alerts(struct sdw_slave *slave) 
static int sdw_update_slave_status(struct sdw_slave *slave,

				   enum sdw_slave_status status)

{

	if (slave->ops && slave->ops->update_status)

		return slave->ops->update_status(slave, status);

	unsigned long time;



	if (!slave->probed) {

		/*

		 * the slave status update is typically handled in an

		 * interrupt thread, which can race with the driver

		 * probe, e.g. when a module needs to be loaded.

		 *

		 * make sure the probe is complete before updating

		 * status.

		 */

		time = wait_for_completion_timeout(&slave->probe_complete,

				msecs_to_jiffies(DEFAULT_PROBE_TIMEOUT));

		if (!time) {

			dev_err(&slave->dev, "Probe not complete, timed out\n");

			return -ETIMEDOUT;

		}

	}



	if (!slave->ops || !slave->ops->update_status)

		return 0;



	return slave->ops->update_status(slave, status);

}



/**

drivers/soundwire/bus.h

+1 −0
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ 
#define __SDW_BUS_H



#define DEFAULT_BANK_SWITCH_TIMEOUT 3000

#define DEFAULT_PROBE_TIMEOUT       2000



#if IS_ENABLED(CONFIG_ACPI)

int sdw_acpi_find_slaves(struct sdw_bus *bus);

drivers/soundwire/bus_type.c

+5 −0
Original line number Diff line number Diff line
@@ -110,6 +110,11 @@ static int sdw_drv_probe(struct device *dev) 
	slave->bus->clk_stop_timeout = max_t(u32, slave->bus->clk_stop_timeout,

					     slave->prop.clk_stop_timeout);



	slave->probed = true;

	complete(&slave->probe_complete);



	dev_dbg(dev, "probe complete\n");



	return 0;

}

drivers/soundwire/slave.c

+2 −0
Original line number Diff line number Diff line
@@ -47,6 +47,8 @@ static int sdw_slave_add(struct sdw_bus *bus, 
	slave->bus = bus;

	slave->status = SDW_SLAVE_UNATTACHED;

	slave->dev_num = 0;

	init_completion(&slave->probe_complete);

	slave->probed = false;



	mutex_lock(&bus->bus_lock);

	list_add_tail(&slave->node, &bus->slaves);