mm: zswap: prevent lruvec release in zswap_folio_swapin()

In the near future, a folio will no longer pin its corresponding
memory cgroup. So an lruvec returned by folio_lruvec() could be
released without the rcu read lock or a reference to its memory
cgroup.

In the current patch, the rcu read lock is employed to safeguard
against the release of the lruvec in zswap_folio_swapin().

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

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

Orabug: 37997580

This suppresses the warning:
  WARNING: CPU: 0 PID: 4240 at include/linux/memcontrol.h:407 zswap_folio_swapin+0x11b/0x160
  [...]
  Call Trace:
   <TASK>
   swap_read_folio+0xec/0x2f0
   swap_cluster_readahead+0x19e/0x310
   do_swap_page+0x216/0x1200
   ? srso_alias_return_thunk+0x5/0xfbef5
   ? lock_acquire+0x107/0x140
   ? __pte_offset_map+0x2a/0x2a0
   ? srso_alias_return_thunk+0x5/0xfbef5
   ? __pfx_default_wake_function+0x10/0x10
   __handle_mm_fault+0x592/0x770
   handle_mm_fault+0x104/0x3a0
   do_user_addr_fault+0x22b/0x7b0
   exc_page_fault+0x77/0x270
   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

mm/zswap.c

@@ -745,8 +745,10 @@ void zswap_folio_swapin(struct folio *folio)
 	struct lruvec *lruvec;
 
 	if (folio) {
+		rcu_read_lock();
 		lruvec = folio_lruvec(folio);
 		atomic_long_inc(&lruvec->zswap_lruvec_state.nr_disk_swapins);
+		rcu_read_unlock();
 	}
 }