From: Kiryl Shutsemau <kas@kernel.org>
To: Sasha Levin <sashal@kernel.org>
Cc: akpm@linux-foundation.org, david@kernel.org,
muchun.song@linux.dev, osalvador@suse.de, peterz@infradead.org,
fvdl@google.com, willy@infradead.org, ljs@kernel.org,
liam@infradead.org, vbabka@kernel.org, rppt@kernel.org,
surenb@google.com, mhocko@suse.com, corbet@lwn.net,
skhan@linuxfoundation.org, rdunlap@infradead.org,
stable@vger.kernel.org
Subject: Re: FAILED: patch "[PATCH] mm/hugetlb_vmemmap: map the shared tail page writable" failed to apply to 6.18-stable tree
Date: Tue, 10 Nov 2026 12:11:44 +0000 [thread overview]
Message-ID: <avMJ1sVDviavKjQu@thinkstation> (raw)
In-Reply-To: <20261109200434-failed-6.18-0120a603afad@kernel.org>
On Mon, Nov 09, 2026 at 08:04:34PM -0500, Sasha Levin wrote:
> The patch below does not apply to the 6.18-stable tree.
It is not needed for 6.18. The bug came with 32c440d67e6c ("mm: drop
fake head checks"), which 6.18 does not have.
But 6.18.y has its sibling, 01b1d0ffb6f7 ("hugetlb: remove
VMEMMAP_SYNCHRONIZE_RCU"), picked up in 6.18.51 as a Stable-dep-of
6e25c6a9c7ef ("mm/hugetlb_vmemmap: fix
__hugetlb_vmemmap_optimize_folios()"). It is only correct once fake
heads are gone. 6.18 still has them, and page_ref_add_unless() still
relies on the synchronize_rcu() it removed, see bd225530a4c7
("mm/hugetlb_vmemmap: fix race with speculative PFN walkers").
So the race bd225530a4c7 fixed is back in 6.18.y: compaction takes a
speculative reference on a PFN, passes page_count_writable() before HVO
remaps the tail vmemmap read-only, does its cmpxchg after the remap and
oopses.
Please revert dba93b8cceb0 from 6.18.y. It reverts cleanly, and
6e25c6a9c7ef applies to 6.18 without it.
--
Kiryl Shutsemau / Kirill A. Shutemov
next prev parent reply other threads:[~2026-11-10 12:11 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-10 1:04 FAILED: patch "[PATCH] mm/hugetlb_vmemmap: map the shared tail page writable" failed to apply to 6.18-stable tree Sasha Levin
2026-11-10 12:11 ` Kiryl Shutsemau [this message]
2026-11-10 20:58 ` Sasha Levin
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