On 2022/03/22 20:10, Christoph Hellwig wrote: > On Wed, Mar 16, 2022 at 10:24:20PM +0900, Tetsuo Handa wrote: >> Since this WQ is invoked when flushing data to disk, this WQ had better use >> WQ_MEM_RECLAIM flag when creating. A WQ created with WQ_MEM_RECLAIM flag has >> at least one "struct task_struct" in order to guarantee forward progress, but >> results in consuming more kernel resources. Therefore, it is preferable to >> destroy the WQ when clearing unbinding a loop device from a backing file. > > Whіch then gets us into lock dependency problems. A previously used > but lingering around device will use some resources, so what? If you > care about the least used resources the only way to get there is to > destroy the device. There is no dependency problems and there is no resource wasting if we choose task_work approach, for that approach runs in lockless context and allows destroying "struct task_struct" as soon as device is unbound.
