FAILED: patch "[PATCH] mm/shmem: don't release a swapin-error marker as a swap entry" failed to apply to 6.18-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.18-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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x e4b92891aaca0d37b5973362dd14747a65406650
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107051044-failed-6.18-e4b92891aaca@kernel.org' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Thanks,
Sasha

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

From e4b92891aaca0d37b5973362dd14747a65406650 Mon Sep 17 00:00:00 2001
From: David Carlier <devnexen@gmail.com>
Date: Sun, 20 Sep 2026 16:50:02 +0100
Subject: [PATCH] mm/shmem: don't release a swapin-error marker as a swap entry

A failed shmem swapin (eg, EIO) frees the swap slot and leaves a
PTE_MARKER_POISONED entry in the page cache.  On truncate or eviction
shmem_free_swap() passes that marker to swap_put_entries_direct(), which
warns because it is not a swap entry.  There is nothing left to release
either way.

Skip the release for non-swap entries, as every other caller already does.

Link: https://lore.kernel.org/20260920155002.1030454-1-devnexen@gmail.com
Fixes: ac2d3268284b ("mm/swapfile.c: remove the unneeded checking")
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: syzbot+23b25ba3c6bf971f9c57@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=23b25ba3c6bf971f9c57
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan he <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chis Li <chrisl@kernel.org> (Google)
Cc: Hugh Dickens <hughd@google.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: <stable@vger.kernel.org>
---
 mm/shmem.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index f2a36a1b53750..07b2855dfb7bd 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1184,6 +1184,7 @@ static long shmem_free_swap(struct address_space *mapping,
 			    pgoff_t index, pgoff_t end, void *radswap)
 {
 	XA_STATE(xas, &mapping->i_pages, index);
+	const softleaf_t swp = radix_to_swp_entry(radswap);
 	unsigned int nr_pages = 0;
 	pgoff_t base;
 	void *entry;
@@ -1200,8 +1201,9 @@ static long shmem_free_swap(struct address_space *mapping,
 	}
 	xas_unlock_irq(&xas);
 
-	if (nr_pages)
-		swap_put_entries_direct(radix_to_swp_entry(radswap), nr_pages);
+	/* A swapin-error marker holds no swap slot, so just drop it. */
+	if (nr_pages && softleaf_is_swap(swp))
+		swap_put_entries_direct(swp, nr_pages);
 
 	return nr_pages;
 }
-- 
2.53.0