From: Matthew Wilcox <willy@infradead.org>
To: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, linmiaohe@huawei.com,
jane.chu@oracle.com, nao.horiguchi@gmail.com, osalvador@suse.de
Subject: Re: [PATCH] mm/memory-failure: remove shake_page()
Date: Fri, 26 Apr 2024 19:27:23 +0100 [thread overview]
Message-ID: <ZivyC3vqa2BIBoMj@casper.infradead.org> (raw)
In-Reply-To: <d05cbf22-f3e8-414a-a2e3-03e0b857eaca@oracle.com>
On Fri, Apr 26, 2024 at 10:57:31AM -0700, Sidhartha Kumar wrote:
> On 4/26/24 10:34 AM, Matthew Wilcox wrote:
> > On Fri, Apr 26, 2024 at 10:15:11AM -0700, Sidhartha Kumar wrote:
> > > Use a folio in get_any_page() to save 5 calls to compound head and
> > > convert the last user of shake_page() to shake_folio(). This allows us
> > > to remove the shake_page() definition.
> >
> > So I didn't do this before because I wasn't convinced it was safe.
> > We don't have a refcount on the folio, so the page might no longer
> > be part of this folio by the time we get the refcount on the folio.
> >
> > I'd really like to see some argumentation for why this is safe.
>
> If I moved down the folio = page_folio() line to after we verify
> __get_hwpoison_page() has returned 1, which indicates the reference count
> was successfully incremented via foliO_try_get(), that means the folio
> conversion would happen after we have a refcount. In the case we don't call
> __get_hwpoison_page(), that means the MF_COUNT_INCREASED flag is set. This
> means the page has existing users so that path would be safe as well. So I
> think this is safe after moving page_folio() after __get_hwpoison_page().
See if you can find a hole in this chain of reasoning ...
memory_failure()
p = pfn_to_online_page(pfn);
res = try_memory_failure_hugetlb(pfn, flags, &hugetlb);
(not a hugetlb)
if (TestSetPageHWPoison(p)) {
(not already poisoned)
if (!(flags & MF_COUNT_INCREASED)) {
res = get_hwpoison_page(p, flags);
get_hwpoison_page()
ret = get_any_page(p, flags);
get_any_page()
folio = page_folio(page)
Because we don't have a reference on the folio at this point (how could
we?), the folio might be split, and now we have a pointer to a folio
which no longer contains the page (assuming we had a hwerror in what
was a tail page at this time).
next prev parent reply other threads:[~2024-04-26 18:27 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 17:15 [PATCH] mm/memory-failure: remove shake_page() Sidhartha Kumar
2024-04-26 17:34 ` Matthew Wilcox
2024-04-26 17:57 ` Sidhartha Kumar
2024-04-26 18:27 ` Matthew Wilcox [this message]
2024-04-26 18:53 ` Sidhartha Kumar
2024-04-26 19:05 ` Matthew Wilcox
2024-04-26 19:52 ` Jane Chu
2024-04-26 20:33 ` Jane Chu
2024-04-28 2:24 ` Miaohe Lin
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