On Mon, Aug 13, 2018 at 10:20 AM Vlad Buslov <vla...@mellanox.com> wrote: > > Lockdep reports deadlock for following locking scenario in ife action: > > Task one: > 1) Executes ife action update. > 2) Takes tcfa_lock. > 3) Waits on ife_mod_lock which is already taken by task two. > > Task two: > > 1) Executes any path that obtains ife_mod_lock without disabling bh (any > path that takes ife_mod_lock while holding tcfa_lock has bh disabled) like > loading a meta module, or creating new action. > 2) Takes ife_mod_lock. > 3) Task is preempted by rate estimator timer. > 4) Timer callback waits on tcfa_lock which is taken by task one. > > In described case tasks deadlock because they take same two locks in > different order. To prevent potential deadlock reported by lockdep, always > disable bh when obtaining ife_mod_lock.
Your fix doesn't make sense, because what ife_mod_lock protects is absolutely not touched in BH context, they have no race. The only time you need tcfa_lock is when adding it to ->metalist: list_add_tail(&mi->metalist, &ife->metalist); when it already exists. Which means you can just take tcfa_lock after taking ife_mod_lock.
