soundwire: revisit driver bind/unbind and callbacks

In the SoundWire probe, we store a pointer from the driver ops into
the 'slave' structure. This can lead to kernel oopses when unbinding
codec drivers, e.g. with the following sequence to remove machine
driver and codec driver.

/sbin/modprobe -r snd_soc_sof_sdw
/sbin/modprobe -r snd_soc_rt711

The full details can be found in the BugLink below, for reference the
two following examples show different cases of driver ops/callbacks
being invoked after the driver .remove().

kernel: BUG: kernel NULL pointer dereference, address: 0000000000000150
kernel: Workqueue: events cdns_update_slave_status_work [soundwire_cadence]
kernel: RIP: 0010:mutex_lock+0x19/0x30
kernel: Call Trace:
kernel:  ? sdw_handle_slave_status+0x426/0xe00 [soundwire_bus 94ff184bf398570c3f8ff7efe9e32529f532e4ae]
kernel:  ? newidle_balance+0x26a/0x400
kernel:  ? cdns_update_slave_status_work+0x1e9/0x200 [soundwire_cadence 1bcf98eebe5ba9833cd433323769ac923c9c6f82]

kernel: BUG: unable to handle page fault for address: ffffffffc07654c8
kernel: Workqueue: pm pm_runtime_work
kernel: RIP: 0010:sdw_bus_prep_clk_stop+0x6f/0x160 [soundwire_bus]
kernel: Call Trace:
kernel:  <TASK>
kernel:  sdw_cdns_clock_stop+0xb5/0x1b0 [soundwire_cadence 1bcf98eebe5ba9833cd433323769ac923c9c6f82]
kernel:  intel_suspend_runtime+0x5f/0x120 [soundwire_intel aca858f7c87048d3152a4a41bb68abb9b663a1dd]
kernel:  ? dpm_sysfs_remove+0x60/0x60

This was not detected earlier in Intel tests since the tests first
remove the parent PCI device and shut down the bus. The sequence
above is a corner case which keeps the bus operational but without a
driver bound.

While trying to solve this kernel oopses, it became clear that the
existing SoundWire bus does not deal well with the unbind case.

Commit 528be501b7d4a ("soundwire: sdw_slave: add probe_complete structure and new fields")
added a 'probed' status variable and a 'probe_complete'
struct completion. This status is however not reset on remove and
likewise the 'probe complete' is not re-initialized, so the
bind/unbind/bind test cases would fail. The timeout used before the
'update_status' callback was also a bad idea in hindsight, there
should really be no timing assumption as to if and when a driver is
bound to a device.

An initial draft was based on device_lock() and device_unlock() was
tested. This proved too complicated, with deadlocks created during the
suspend-resume sequences, which also use the same device_lock/unlock()
as the bind/unbind sequences. On a CometLake device, a bad DSDT/BIOS
caused spurious resumes and the use of device_lock() caused hangs
during suspend. After multiple weeks or testing and painful
reverse-engineering of deadlocks on different devices, we looked for
alternatives that did not interfere with the device core.

A bus notifier was used successfully to keep track of DRIVER_BOUND and
DRIVER_UNBIND events. This solved the bind-unbind-bind case in tests,
but it can still be defeated with a theoretical corner case where the
memory is freed by a .remove while the callback is in use. The
notifier only helps make sure the driver callbacks are valid, but not
that the memory allocated in probe remains valid while the callbacks
are invoked.

This patch suggests the introduction of a new 'sdw_dev_lock' mutex
protecting probe/remove and all driver callbacks. Since this mutex is
'local' to SoundWire only, it does not interfere with existing locks
and does not create deadlocks. In addition, this patch removes the
'probe_complete' completion, instead we directly invoke the
'update_status' from the probe routine. That removes any sort of
timing dependency and a much better support for the device/driver
model, the driver could be bound before the bus started, or eons after
the bus started and the hardware would be properly initialized in all
cases.

BugLink: https://github.com/thesofproject/linux/issues/3531
Fixes: 56d4fe31af77 ("soundwire: Add MIPI DisCo property helpers")
Fixes: 528be501b7d4a ("soundwire: sdw_slave: add probe_complete structure and new fields")
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Link: https://lore.kernel.org/r/20220621225641.221170-2-pierre-louis.bossart@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

1 files changed, 2 insertions, 4 deletions

diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
index 76ce3f3ac0f2..bf6f0decb3f6 100644
--- a/include/linux/soundwire/sdw.h
+++ b/include/linux/soundwire/sdw.h
@@ -646,9 +646,6 @@ struct sdw_slave_ops {
  * @dev_num: Current Device Number, values can be 0 or dev_num_sticky
  * @dev_num_sticky: one-time static Device Number assigned by Bus
  * @probed: boolean tracking driver state
- * @probe_complete: completion utility to control potential races
- * on startup between driver probe/initialization and SoundWire
- * Slave state changes/implementation-defined interrupts
  * @enumeration_complete: completion utility to control potential races
  * on startup between device enumeration and read/write access to the
  * Slave device
@@ -663,6 +660,7 @@ struct sdw_slave_ops {
  * for a Slave happens for the first time after enumeration
  * @is_mockup_device: status flag used to squelch errors in the command/control
  * protocol for SoundWire mockup devices
+ * @sdw_dev_lock: mutex used to protect callbacks/remove races
  */
 struct sdw_slave {
 	struct sdw_slave_id id;
@@ -680,12 +678,12 @@ struct sdw_slave {
 	u16 dev_num;
 	u16 dev_num_sticky;
 	bool probed;
-	struct completion probe_complete;
 	struct completion enumeration_complete;
 	struct completion initialization_complete;
 	u32 unattach_request;
 	bool first_interrupt_done;
 	bool is_mockup_device;
+	struct mutex sdw_dev_lock; /* protect callbacks/remove races */
 };
 
 #define dev_to_sdw_dev(_dev) container_of(_dev, struct sdw_slave, dev)