On 11/2/2016 6:30 PM, Jike Song wrote: > On 11/02/2016 08:41 PM, Kirti Wankhede wrote: >> On 11/2/2016 5:51 PM, Jike Song wrote: >>> On 11/02/2016 12:09 PM, Alexey Kardashevskiy wrote: >>>> Or you could just reference and use @mm as KVM and others do. Or there is >>>> anything else you need from @current than just @mm? >>>> >>> >>> I agree. If @mm is the only thing needed, there is really no reason to >>> refer to the @task :-) >>> >> >> In vfio_lock_acct(), that is for page accounting, if mm->mmap_sem is >> already held then page accounting is deferred, where task structure is >> used to get mm and work is deferred only if mm exist: >> mm = get_task_mm(task); >> >> That is where this module need task structure. > > Kirti, > > By calling get_task_mm you hold a ref on @mm and save it in iommu, > whenever you want to do something like vfio_lock_acct(), use that mm > (as you said, if mmap_sem not accessible then defer it to a work, but > still @mm is the whole information), and put it after the usage. > > I still can't see any reason that the @task have to be saved. It's > always the @mm all the time. Did I miss anything? > If the process is terminated by SIGKILL, as Alexey mentioned in this mail thread earlier exit_mm() is called first and then all files are closed. From exit_mm(), task->mm is set to NULL. So from teardown path, we should call get_task_mm(task) to get current status intsead of using stale pointer. Thanks, Kirti. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
