FAILED: patch "[PATCH] mm: memcg: fix NULL pointer in" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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 <[email protected]>.

Possible dependencies:

ac86f547ca10 ("mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty_slowpath()") 203a31516616 ("mm/writeback: Add __folio_mark_dirty()")
9d8053fc7a21 ("mm/memcg: Convert mem_cgroup_track_foreign_dirty_slowpath() to folio") a49d0c507759 ("mm/writeback: Add folio_wait_stable()")
490e016f229a ("mm/writeback: Add folio_wait_writeback()")
4268b48077e5 ("mm/filemap: Add folio_end_writeback()")
575ced1c8b0d ("mm/swap: Add folio_rotate_reclaimable()")
4e1364286d0a ("mm/filemap: Add folio_unlock()")
2f52578f9c64 ("mm/util: Add folio_mapping() and folio_file_mapping()")

thanks,

greg k-h

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

From ac86f547ca1002aec2ef66b9e64d03f45bbbfbb9 Mon Sep 17 00:00:00 2001
From: Kefeng Wang <[email protected]>
Date: Sun, 29 Jan 2023 12:09:45 +0800
Subject: [PATCH] mm: memcg: fix NULL pointer in
mem_cgroup_track_foreign_dirty_slowpath()

As commit 18365225f044 ("hwpoison, memcg: forcibly uncharge LRU pages"), hwpoison will forcibly uncharg a LRU hwpoisoned page, the folio_memcg could be NULl, then, mem_cgroup_track_foreign_dirty_slowpath() could occurs a NULL pointer dereference, let's do not record the foreign writebacks for folio memcg is null in mem_cgroup_track_foreign_dirty() to fix it.

index d3c8203cab6c..85dc9b88ea37 100644
@@ -1666,10 +1666,13 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct folio *folio,
 static inline void mem_cgroup_track_foreign_dirty(struct folio *folio,
 						  struct bdi_writeback *wb)
 {
+	struct mem_cgroup *memcg;
+
 	if (mem_cgroup_disabled())
 		return;
 
-	if (unlikely(&folio_memcg(folio)->css != wb->memcg_css))
+	memcg = folio_memcg(folio);
+	if (unlikely(memcg && &memcg->css != wb->memcg_css))
 		mem_cgroup_track_foreign_dirty_slowpath(folio, wb);
 }