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soundwire: bus: fix race condition with probe_complete signaling

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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>
This commit is contained in:
Pierre-Louis Bossart 2020-01-14 18:08:35 -06:00 committed by Vinod Koul
parent eff346f24b
commit 2140b66b5d
4 changed files with 30 additions and 3 deletions
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25
drivers/soundwire/bus.c
View file

@ -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);
}
/**

1
drivers/soundwire/bus.h
View file

@ -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);

5
drivers/soundwire/bus_type.c
View file

@ -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;
}

2
drivers/soundwire/slave.c
View file

@ -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);