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The lifetime of address handler has been managed by linked list and RCU. This approach was introduced in commit35202f7d84("firewire: remove global lock around address handlers, convert to RCU"). The invocations of address handler are performed within RCU read-side critical sections. In commit57e6d9f85f("firewire: ohci: use workqueue to handle events of AR request/response contexts"), the invocations are in a workqueue context. The approach still imposes limitation that sleeping is not allowed within RCU read-side critical sections. However, since sleeping is not permitted within RCU read-side critical sections, this approach still has a limitation. This commit adds reference counting to decouple handler invocation from handler discovery. The linked list and RCU is used to discover the handlers, while the reference counting is used to invoke them safely. Link: https://lore.kernel.org/r/20250803122015.236493-2-o-takashi@sakamocchi.jp Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>