On 2023/02/05 0:12, Alan Stern wrote: >> it would solve many deadlocks in driver code if you can update > > What deadlocks? If there are so many deadlocks floating around in > driver code, why haven't we heard about them before now? Since dev->mutex is hidden from lockdep checks, nobody can see lockdep warnings. syzbot is reporting real deadlocks without lockdep warnings, for the fundamental problem you mentioned in https://lkml.kernel.org/r/Pine.LNX.4.44L0.0804171117450.18040-100000@xxxxxxxxxxxxxxxxxxxx is remaining. I'm suggesting you that now is time to address this fundamental problem. >> (by e.g. replacing dev->mutex with dev->spinlock and dev->atomic_flags). >> But I'm not familiar enough to propose such change... > > Such a change cannot be made. Consider this: Driver callbacks often > need to sleep. But when a thread holds a spinlock, it is not allowed to > sleep. Therefore driver callbacks must not be invoked while a spinlock > is held. What I'm suggesting is "Do not call driver callbacks with dev->mutex held, by rewriting driver core code".
