Re: [PATCH v7 6/7] mm/madvise: employ mmget_still_valid for write lock

[Oleksandr Natalenko]

On Fri, Mar 06, 2020 at 05:03:50PM +0100, Vlastimil Babka wrote:
> On 3/6/20 2:03 PM, Oleksandr Natalenko wrote:
> > Hello.
> > 
> > On Fri, Mar 06, 2020 at 01:52:07PM +0100, Vlastimil Babka wrote:
> >> > diff --git a/mm/madvise.c b/mm/madvise.c
> >> > index e794367f681e..e77c6c1fad34 100644
> >> > --- a/mm/madvise.c
> >> > +++ b/mm/madvise.c
> >> > @@ -1118,6 +1118,8 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
> >> >  	if (write) {
> >> >  		if (down_write_killable(&mm->mmap_sem))
> >> >  			return -EINTR;
> >> > +		if (current->mm != mm && !mmget_still_valid(mm))
> >> > +			goto skip_mm;
> >> 
> >> This will return 0, is that correct? Shoudln't there be a similar error e.g. as
> >> when finding the task by pid fails (-ESRCH ?), because IIUC the task here is
> >> going away and dumping the core?
> > 
> > Yeah.
> > 
> > Something like this then:
> > 
> > ===
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index 48d1da08c160..7ed2f4d13924 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -1122,6 +1122,10 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
> >  	if (write) {
> >  		if (down_write_killable(&mm->mmap_sem))
> >  			return -EINTR;
> > +		if (current->mm != mm && !mmget_still_valid(mm)) {
> > +			error = -ESRCH;
> > +			goto skip_mm;
> > +		}
> >  	} else {
> >  		down_read(&mm->mmap_sem);
> >  	}
> > @@ -1173,6 +1177,7 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
> >  	}
> >  out:
> >  	blk_finish_plug(&plug);
> > +skip_mm:
> >  	if (write)
> >  		up_write(&mm->mmap_sem);
> >  	else
> > 
> > ===
> > 
> > ?
> 
> Yep, thanks.
> 

Minchan, shall you take this change into the next submission, or you'd
prefer me sending it to you as a new patch?

-- 
  Best regards,
    Oleksandr Natalenko (post-factum)
    Principal Software Maintenance Engineer