On Fri 12-02-21 21:58:15, Tetsuo Handa wrote: > On 2021/02/12 21:30, Michal Hocko wrote: > > On Fri 12-02-21 12:22:07, Matthew Wilcox wrote: > >> On Fri, Feb 12, 2021 at 08:18:11PM +0900, Tetsuo Handa wrote: > >>> On 2021/02/12 1:41, Michal Hocko wrote: > >>>> But I suspect we have drifted away from the original issue. I thought > >>>> that a simple check would help us narrow down this particular case and > >>>> somebody messing up from the IRQ context didn't sound like a completely > >>>> off. > >>>> > >>> > >>> From my experience at https://lkml.kernel.org/r/201409192053.IHJ35462.JLOMOSOFFVtQFH@xxxxxxxxxxxxxxxxxxx , > >>> I think we can replace direct PF_* manipulation with macros which do not receive "struct task_struct *" argument. > >>> Since TASK_PFA_TEST()/TASK_PFA_SET()/TASK_PFA_CLEAR() are for manipulating PFA_* flags on a remote thread, we can > >>> define similar ones for manipulating PF_* flags on current thread. Then, auditing dangerous users becomes easier. > >> > >> No, nobody is manipulating another task's GFP flags. > > > > Agreed. And nobody should be manipulating PF flags on remote tasks > > either. > > > > No. You are misunderstanding. The bug report above is an example of > manipulating PF flags on remote tasks. The bug report you are referring to is ancient. And the cpuset code doesn't touch task->flags for a long time. I haven't checked exactly but it is years since regular and atomic flags have been separated unless I misremember. > You say "nobody should", but the reality is "there indeed was". There > might be unnoticed others. The point of this proposal is to make it > possible to "find such unnoticed users who are manipulating PF flags > on remote tasks". I am really confused what you are proposing here TBH and referring to an ancient bug doesn't really help. task->flags are _explicitly_ documented to be only used for _current_. Is it possible that somebody writes a buggy code? Sure, should we build a whole infrastructure around that to catch such a broken code? I am not really sure. One bug 6 years ago doesn't sound like a good reason for that. -- Michal Hocko SUSE Labs
