linux-kernel - Re: [PATCH v4 4/4] selftests/mm: add tests for HWPOISON hugetlbfs read

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Message-ID: <ZaAtjVVTETdQDR4B@casper.infradead.org>
Date: Thu, 11 Jan 2024 18:03:57 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc: Jiaqi Yan <jiaqiyan@...gle.com>,
	Muhammad Usama Anjum <usama.anjum@...labora.com>,
	linmiaohe@...wei.com, mike.kravetz@...cle.com,
	naoya.horiguchi@....com, akpm@...ux-foundation.org,
	songmuchun@...edance.com, shy828301@...il.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, jthoughton@...gle.com,
	"kernel@...labora.com" <kernel@...labora.com>
Subject: Re: [PATCH v4 4/4] selftests/mm: add tests for HWPOISON hugetlbfs
 read

On Thu, Jan 11, 2024 at 09:51:47AM -0800, Sidhartha Kumar wrote:
> On 1/11/24 9:34 AM, Jiaqi Yan wrote:
> > > -                       if (!folio_test_has_hwpoisoned(folio))
> > > +                       if (!folio_test_hwpoison(folio))
> > 
> > Sidhartha, just curious why this change is needed? Does
> > PageHasHWPoisoned change after commit
> > "a08c7193e4f18dc8508f2d07d0de2c5b94cb39a3"?
> 
> No its not an issue PageHasHWPoisoned(), the original code is testing for
> the wrong flag and I realized that has_hwpoison and hwpoison are two
> different flags. The memory-failure code calls folio_test_set_hwpoison() to
> set the hwpoison flag and does not set the has_hwpoison flag. When
> debugging, I realized this if statement was never true despite the code
> hitting folio_test_set_hwpoison(). Now we are testing the correct flag.
> 
> From page-flags.h
> 
> #ifdef CONFIG_MEMORY_FAILURE
> 	PG_hwpoison,		/* hardware poisoned page. Don't touch */
> #endif
> 
> folio_test_hwpoison() checks this flag ^^^
> 
> /* At least one page in this folio has the hwpoison flag set */
> PG_has_hwpoisoned = PG_error,
> 
> while folio_test_has_hwpoisoned() checks this flag ^^^

So what you're saying is that hugetlb behaves differently from THP
with how memory-failure sets the flags?