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Mika Westerberg authored
switch_lock was introduced because it allowed serialization of device authorization requests from userspace without need to take the big domain lock (tb->lock). This was fine because device authorization with ICM is just one command that is sent to the firmware. Now that we start to handle all tunneling in the driver switch_lock is not enough because we need to walk over the topology to establish paths. For this reason drop switch_lock from the driver completely in favour of big domain lock. There is one complication, though. If userspace is waiting for the lock in tb_switch_set_authorized(), it keeps the device_del() from removing the sysfs attribute because it waits for active users to release the attribute first which leads into following splat: INFO: task kworker/u8:3:73 blocked for more than 61 seconds. Tainted: G W 5.1.0-rc1+ #244 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. kworker/u8:3 D12976 73 2 0x80000000 Workqueue: thunderbolt0 tb_handle_hotplug [thunderbolt] Call Trace: ? __schedule+0x2e5/0x740 ? _raw_spin_lock_irqsave+0x12/0x40 ? prepare_to_wait_event+0xc5/0x160 schedule+0x2d/0x80 __kernfs_remove.part.17+0x183/0x1f0 ? finish_wait+0x80/0x80 kernfs_remove_by_name_ns+0x4a/0x90 remove_files.isra.1+0x2b/0x60 sysfs_remove_group+0x38/0x80 sysfs_remove_groups+0x24/0x40 device_remove_attrs+0x3d/0x70 device_del+0x14c/0x360 device_unregister+0x15/0x50 tb_switch_remove+0x9e/0x1d0 [thunderbolt] tb_handle_hotplug+0x119/0x5a0 [thunderbolt] ? process_one_work+0x1b7/0x420 process_one_work+0x1b7/0x420 worker_thread+0x37/0x380 ? _raw_spin_unlock_irqrestore+0xf/0x30 ? process_one_work+0x420/0x420 kthread+0x118/0x130 ? kthread_create_on_node+0x60/0x60 ret_from_fork+0x35/0x40 We deal this by following what network stack did for some of their attributes and use mutex_trylock() with restart_syscall(). This makes userspace release the attribute allowing sysfs attribute removal to progress before the write is restarted and eventually fail when the attribute is removed. Signed-off-by:
Mika Westerberg <mika.westerberg@linux.intel.com>
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