mm: page_io: prevent memory cgroup release in page_io 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 rcu read lock is employed to safeguard
against the release of the memory cgroup in swap_writepage() and
bio_associate_blkg_from_page().

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

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

Orabug: 37997580

Conflicts:
	mm/page_io.c

	While converting bio_associate_blkg_from_page() was converted in
	the commit 4717687 ("mm: memcontrol: make all the callers of
	{folio,page}_memcg() safe"), swap_writepage() was not converted.

This suppresses the warning:
  WARNING: CPU: 0 PID: 56 at include/linux/memcontrol.h:407 swap_writepage+0x255/0x280
  [...]
  Call Trace:
   <TASK>
   pageout+0x163/0x370
   shrink_folio_list+0x7c6/0x10a0
   shrink_inactive_list+0x185/0x4f0
   shrink_lruvec+0x3a0/0x4b0
   ? __lock_release.isra.0+0x66/0x180
   ? percpu_ref_put_many.constprop.0+0x5d/0x110
   shrink_node_memcgs+0x1db/0x270
   shrink_node+0x11d/0x420
   ? srso_alias_return_thunk+0x5/0xfbef5
   ? lock_acquire+0x107/0x140
   ? balance_pgdat+0x30f/0x750
   balance_pgdat+0x28d/0x750
   kswapd+0xf8/0x1d0
   ? __pfx_kswapd+0x10/0x10
   kthread+0xd6/0x110
   ? __pfx_kthread+0x10/0x10
   ret_from_fork+0x34/0x50
   ? __pfx_kthread+0x10/0x10
   ret_from_fork_asm+0x1a/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

mm/page_io.c

@@ -280,10 +280,14 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		folio_unlock(folio);
 		return 0;
 	}
+
+	rcu_read_lock();
 	if (!mem_cgroup_zswap_writeback_enabled(folio_memcg(folio))) {
+		rcu_read_unlock();
 		folio_mark_dirty(folio);
 		return AOP_WRITEPAGE_ACTIVATE;
 	}
+	rcu_read_unlock();
 
 	__swap_writepage(folio, wbc);
 	return 0;