[PATCH 6.18.y] mm/shmem: don't release a swapin-error marker as a swap entry

[Sasha Levin <sashal@kernel.org>]

From: David Carlier <devnexen@gmail.com>

[ Upstream commit e4b92891aaca0d37b5973362dd14747a65406650 ]

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>
[ sashal: adapted newer softleaf and swap-release APIs to the existing swp_entry_t-based swap helpers ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/shmem.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 5efde9fcc3057..d90225a3b9a4d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -947,6 +947,7 @@ 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 swp_entry_t swp = radix_to_swp_entry(radswap);
 	unsigned int nr_pages = 0;
 	pgoff_t base;
 	void *entry;
@@ -963,8 +964,9 @@ static long shmem_free_swap(struct address_space *mapping,
 	}
 	xas_unlock_irq(&xas);
 
-	if (nr_pages)
-		free_swap_and_cache_nr(radix_to_swp_entry(radswap), nr_pages);
+	/* A swapin-error marker holds no swap slot, so just drop it. */
+	if (nr_pages && !non_swap_entry(swp))
+		free_swap_and_cache_nr(swp, nr_pages);
 
 	return nr_pages;
 }
-- 
2.53.0