Re: [PATCH 13/18] exec: make exec path waiting for mmap_sem killable

[Michal Hocko]

On Mon 29-02-16 18:23:34, Oleg Nesterov wrote:
> On 02/29, Michal Hocko wrote:
> >
> > @@ -267,7 +267,10 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
> >  	if (!vma)
> >  		return -ENOMEM;
> >  
> > -	down_write(&mm->mmap_sem);
> > +	if (down_write_killable(&mm->mmap_sem)) {
> > +		err = -EINTR;
> > +		goto err_free;
> > +	}
> >  	vma->vm_mm = mm;
> 
> I won't argue, but this looks unnecessary. Nobody else can see this new mm,
> down_write() can't block.
> 
> In fact I think we can just remove down_write/up_write here. Except perhaps
> there is lockdep_assert_held() somewhere in these paths.

This is what I had initially but then I've noticed that mm_alloc() does
mm_init(current)->init_new_context(current) so the outside can see this
mm AFAICS. Now I guess this shouldn't matter in the real life but the
code doesn't seem much harder to follow, the callers are already
handling all error paths so I guess it would be better to simply move on
this. Or am I misunderstanding the code or missing something?

-- 
Michal Hocko
SUSE Labs