Hello, On Tue, Dec 20, 2022 at 05:19:12PM +0800, Yu Kuai wrote: > Yes, that sounds good. BTW, queue_lock is also used to protect > pd_alloc_fn/pd_init_fn，and we found that blkcg_activate_policy() is > problematic: > > blkcg_activate_policy > spin_lock_irq(&q->queue_lock); > list_for_each_entry_reverse(blkg, &q->blkg_list > pd_alloc_fn(GFP_NOWAIT | __GFP_NOWARN,...) -> failed > > spin_unlock_irq(&q->queue_lock); > // release queue_lock here is problematic, this will cause > pd_offline_fn called without pd_init_fn. > pd_alloc_fn(__GFP_NOWARN,...) So, if a blkg is destroyed while a policy is being activated, right? > If we are using a mutex to protect rq_qos ops, it seems the right thing > to do do also using the mutex to protect blkcg_policy ops, and this > problem can be fixed because mutex can be held to alloc memroy with > GFP_KERNEL. What do you think? One worry is that switching to mutex can be more headache due to destroy path synchronization. Another approach would be using a per-blkg flag to track whether a blkg has been initialized. Thanks. -- tejun
