FAILED: patch "[PATCH] mm/huge_memory: fix truncate racing with PMD zapping" failed to apply to 6.12-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x e6a07d29b0a60f3a4cfe77fe34eeb4b3fb38d6c4
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261109200855-failed-6.12-e6a07d29b0a6@kernel.org' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From e6a07d29b0a60f3a4cfe77fe34eeb4b3fb38d6c4 Mon Sep 17 00:00:00 2001
From: Chris Mason <mason@kernel.org>
Date: Sat, 31 Oct 2026 10:39:42 +0100
Subject: [PATCH] mm/huge_memory: fix truncate racing with PMD zapping

zap_huge_pmd_folio() removes the rmap before calling folio_mark_dirty().
If this was the last mapping, truncation can skip unmapping the folio
and proceed without waiting for the PMD lock, racing with dirtying.

ifs_set_range_dirty() can oops if MADV_DONTNEED races with
ftruncate() on XFS, when we get the folio set dirty after it was found
to not be mapped anymore.

Move folio_mark_dirty() and folio_mark_accessed() before rmap removal,
matching the PTE zap path. This keeps the folio mapped while updating
its state, so truncation must wait for the page table lock.

Fix generated by an LLM and sent by Chris Mason in private.

Fixes: fe6cf984939d ("mm/huge_memory: transfer the pmd dirty bit to the folio on zap")
Cc: stable@vger.kernel.org
Signed-off-by: Chris Mason <mason@kernel.org>
[ david: simplify comment and description ]
Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Link: https://patch.msgid.link/20261031-fixes_core-v3-13-d6437171ecc3@kernel.org
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/huge_memory.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 283c4bc8b927c..ce52962db16b9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2495,10 +2495,6 @@ static void zap_huge_pmd_folio(struct mm_struct *mm, struct vm_area_struct *vma,
 {
 	const bool is_device_private = folio_is_device_private(folio);
 
-	/* Present and device private folios are rmappable. */
-	if (is_present || is_device_private)
-		folio_remove_rmap_pmd(folio, &folio->page, vma);
-
 	if (folio_test_anon(folio)) {
 		add_mm_counter(mm, MM_ANONPAGES, -HPAGE_PMD_NR);
 	} else {
@@ -2512,6 +2508,13 @@ static void zap_huge_pmd_folio(struct mm_struct *mm, struct vm_area_struct *vma,
 			folio_mark_accessed(folio);
 	}
 
+	/*
+	 * Present and device private folios are rmappable. Remove the
+	 * rmap after transferring young+dirty to the folio.
+	 */
+	if (is_present || is_device_private)
+		folio_remove_rmap_pmd(folio, &folio->page, vma);
+
 	/* Device private folios are pinned. */
 	if (is_device_private)
 		folio_put(folio);
-- 
2.53.0