writeback: prevent memory cgroup release in writeback module

In the near future, a folio will no longer pin its corresponding
memory cgroup. To ensure safety, it will only be appropriate to
hold the rcu read lock or acquire a reference to the memory cgroup
returned by folio_memcg(), thereby preventing it from being released.

In the current patch, the function get_mem_cgroup_css_from_folio()
and the rcu read lock are employed to safeguard against the release
of the memory cgroup.

This serves as a preparatory measure for the reparenting of the
LRU pages.

Signed-off-by: Muchun Song <[email protected]>

Orabug: 37997580

Conflicts:
	include/trace/events/writeback.h
	mm/memcontrol.c
	fs/fs-writeback.c

	Most of the functions were already converted by the commit
	4717687 ("mm: memcontrol: make all the callers of
	{folio,page}_memcg() safe"), mem_cgroup_track_foreign_dirty()
	was not converted.

This suppresses the warning:
  WARNING: CPU: 0 PID: 638 at include/linux/memcontrol.h:407 folio_account_dirtied+0x2a8/0x2e0
  [...]
  Call Trace:
   <TASK>
   __folio_mark_dirty+0x3e/0xb0
   filemap_dirty_folio+0x61/0xa0
   iomap_page_mkwrite+0x1c8/0x2f0
   xfs_write_fault+0x1cc/0x2f0 [xfs]
   ? __xfs_filemap_fault+0x39/0x1a0 [xfs]
   do_page_mkwrite+0x45/0xf0
   do_wp_page+0xe5/0x760
   __handle_mm_fault+0x58f/0x770
   handle_mm_fault+0xde/0x390
   do_user_addr_fault+0x1b9/0x640
   exc_page_fault+0x76/0x210
   asm_exc_page_fault+0x26/0x30
   </TASK>

Link: https://lore.kernel.org/linux-mm/[email protected]/
Fixes: 4717687 ("mm: memcontrol: make all the callers of {folio,page}_memcg() safe")
Reviewed-by: Imran Khan <[email protected]>
Signed-off-by: Harry Yoo <[email protected]>

Author: Muchun Song

include/linux/memcontrol.h

@@ -1657,9 +1657,14 @@ static inline void mem_cgroup_track_foreign_dirty(struct folio *folio,
 	if (mem_cgroup_disabled())
 		return;
 
+	if (!folio_memcg_charged(folio))
+		return;
+
+	rcu_read_lock();
 	memcg = folio_memcg(folio);
-	if (unlikely(memcg && &memcg->css != wb->memcg_css))
+	if (unlikely(&memcg->css != wb->memcg_css))
 		mem_cgroup_track_foreign_dirty_slowpath(folio, wb);
+	rcu_read_unlock();
 }
 
 void mem_cgroup_flush_foreign(struct bdi_writeback *wb);