Re: [PATCH v2 2/2] mm: Use vma_start_write_killable() in dup_mmap()

[Matthew Wilcox <willy@infradead.org>]

On Thu, Nov 13, 2025 at 01:25:40PM +0000, Lorenzo Stoakes wrote:
> On Mon, Nov 10, 2025 at 08:32:02PM +0000, Matthew Wilcox (Oracle) wrote:
> > Allow waiting for the VMA write lock to be interrupted by fatal signals.
> > The explicit check for fatal_signal_pending() can be removed as it
> > is checked during vma_start_write_killable().  Improves the latency
> > of killing the task as we do not wait for the reader to finish before
> > checking for signals.
> 
> Does this fix Chris's issues or is a forthcoming series required for that?
> I'm guessing not, as his issue was w.r.t. reclaim right rather than at the
> point of forking?
> 
> If it does we should say so I think. If not then obviously not!

No, it won't fix Chris's issue.  I just wanted to have one user in tree
(which was a good idea because syzbot promptly caught the lockdep bug).
This one is an obvious one which already has a good fallback path.
Most of the other places need a fallback path written, which requires
more time and attention than I can devote to the task right now.

> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Thanks!

> > -		vma_start_write(mpnt);
> > +		retval = vma_start_write_killable(mpnt);
> 
> Maybe worth explicitly adding a comment to say we handle fatal signals
> here? I guess it is implied but still maybe useful?

I think that would be over-commenting, tbh.