On Tue, Dec 24, 2024 at 06:51:27PM +0800, Lin Ma wrote: > Hello Leon, > > > > > I'm not fully understand the lockdep here. We use down_read(), which is > > reentry safe. > > > > Really? To my knowledge, though down_read() itself will not trigger locking > errors. But below scenario will lead to deadlock, and that's why this > WARNING is raised. > > CPU0 CPU1 > ---- ---- > down_read()[1] > down_write()[2] > down_read()[3] > > If CPU1 thread not exists, the CPU0 will run smoothly (However, it will keep > looping and the PoC cannot be killed by any signal, causing Denial-of-Service). > > When CPU1 calls down_write(), it will wait for [1] to be released. > However, when [3] is called, it will then wait for [2] to be released, > leading to a deadlock situation. > > Please let me know if I understand this correctly or incorrectly? The thing is that down_write() is called when we unregistering module which sent netlink messages. It shouldn't happen. Thanks > > Thanks, > Lin
