Hello, On Fri, Mar 18, 2022 at 09:05:42PM +0900, Tetsuo Handa wrote: > But since include/linux/workqueue.h only says > > __WQ_LEGACY = 1 << 18, /* internal: create*_workqueue() */ > > , I can't tell when not to specify __WQ_LEGACY and WQ_MEM_RECLAIM together... > > Tejun, what is the intent of this warning? Can the description of __WQ_LEGACY flag > be updated? I think that the loop module had better reserve one "struct task_struct" > for each loop device. > > I guess that, in general, waiting for a work in !WQ_MEM_RECLAIM WQ from a > WQ_MEM_RECLAIM WQ is dangerous because that work may not be able to find > "struct task_struct" for processing that work. Then, what we should do is to > create mp->m_sync_workqueue with WQ_MEM_RECLAIM flag added instead of creating > lo->workqueue with __WQ_LEGACY + WQ_MEM_RECLAIM flags added... > > Is __WQ_LEGACY + WQ_MEM_RECLAIM combination a hack for silencing this warning > without fixing various WQs used by xfs and other filesystems? So, create_workqueue() is the deprecated interface and always imples MEM_RECLAIM because back when the interface was added each wq had a dedicated worker and there's no way to tell one way or the other. The warning is telling you to convert the workqueue to the alloc_workqueue() interface and explicitly use WQ_MEM_RECLAIM flag if the workqueue is gonna participate in MEM_RECLAIM chain. Thanks. -- tejun
