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

[Minchan Kim <minchan@kernel.org>]

On Mon, Mar 09, 2020 at 01:30:45PM +0100, Oleksandr Natalenko wrote:
> 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?

I should send patchset again so I will take it.
Thanks!