On Mon, 28 Mar 2022 15:09:33 +0530, Viresh Kumar wrote: > On 28-03-22, 17:13, Xiaomeng Tong wrote: > > On Mon, 28 Mar 2022 14:20:57 +0530, Viresh Kumar wrote: > > > On 28-03-22, 15:43, Xiaomeng Tong wrote: > > > > No. the conditon to call opp_migrate_dentry(opp_dev, opp_table); is: > > > > if (!list_is_singular(&opp_table->dev_list)), > > > > > > > > while list_is_singlular is: !list_empty(head) && (head->next == head->prev); > > > > > > > > so the condition is: list_empty(head) || (head->next != head->prev) > > > > > > > > if the list is empty, the bug can be triggered. > > > > > > List can't be empty here by design. It will be a huge bug in that > > > case, which should lead to crash somewhere. > > > > > > > There is anther condition to trigger this bug: the list is not empty and > > no element found (if (iter != opp_dev)). > > I suggest reading the code again, considering opp_debug_unregister() > as well. > > What's happening here is this: > > - Several devices share the OPP table. > - One of them (devX) is going away and opp_debug_unregister() is called for this device. > - If devX is the last device for this OPP table, then we don't migrate > and just release all resources. > - Otherwise, we migrate it to the next element in the list. i.e. any > device which != devX. > > Please tell based on this where do you see a possibility of a bug. > Surely there can be one, but I fail to see it at the moment and need > more detail of the same. > Perhaps you are right. Anyway, It is a good choise to use list iterator only inside the loop as linus suggested [1], to avoid potential risk. I have also repost another patch with changed commit message. Please check it, thank you. [1]:https://lore.kernel.org/lkml/20220301075839.4156-1-xiam0nd.tong@xxxxxxxxx/ -- Xiaomeng Tong
