Re: [PATCH] mm/huge_memory: set PG_has_hwpoisoned only after new folio head is established

[Rik van Riel <riel@surriel.com>]

On Wed, 2026-07-01 at 15:52 +0100, Lorenzo Stoakes wrote:
> On Wed, Jul 01, 2026 at 09:46:22AM -0400, Rik van Riel wrote:
> > 
> > @@ -3612,6 +3608,18 @@ static void __split_folio_to_order(struct
> > folio *folio, int old_order,
> >  			folio_set_large_rmappable(new_folio);
> >  		}
> > 
> > +		/*
> > +		 * PG_has_hwpoisoned is a FOLIO_SECOND_PAGE flag,
> > so it can only
> > +		 * be set once @new_folio is a real (head) folio. 
> > Defer setting
> > +		 * it until after
> > clear_compound_head()/prep_compound_page() have
> > +		 * turned @new_head from a tail page into a proper
> > folio head;
> > +		 * otherwise folio_flags() trips on (page-
> > >compound_info & 1).
> > +		 * handle_hwpoison implies new_order != 0.
> > +		 */
> 
> This reads like an LLM comment...! A ton of noise and unnecessary
> detail.
> 
> How about:
> 
> 		/*
> 		 * PG_has_hwpoisoned is on the 2nd page, so set it
> after
> 		 * compound head prepped.
> 		 */

It was an LLM comment, indeed. I harvest these
syzkaller fixes from an automated run every
once in a while, where the fix is "verified"
by checking whether the issue can still reproduce
after a tentative fix has been applied.

I've fixed up the comment as suggested, and
will CC: stable@kernel.org on v2.

thank you for the review,

Rik
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