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: Rander Wang <rander.wang@intel.com>
Signed-off-by: Pierre-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: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index 6106577..4980dfd 100644 (file)
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -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;
 
-       return 0;
+       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);
 }
 
 /**

diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
index cb482da..acb8d11 100644 (file)
--- a/drivers/soundwire/bus.h
+++ b/drivers/soundwire/bus.h
@@ -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);

diff --git a/drivers/soundwire/bus_type.c b/drivers/soundwire/bus_type.c
index 4a465f5..17f096d 100644 (file)
--- a/drivers/soundwire/bus_type.c
+++ b/drivers/soundwire/bus_type.c
@@ -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;
 }
 

diff --git a/drivers/soundwire/slave.c b/drivers/soundwire/slave.c
index 1991997..08db048 100644 (file)
--- a/drivers/soundwire/slave.c
+++ b/drivers/soundwire/slave.c
@@ -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);