+ mm-zswap-dont-return-lru_skip-if-we-have-dropped-lru-lock.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/zswap: don't return LRU_SKIP if we have dropped lru lock
has been added to the -mm mm-unstable branch.  Its filename is
     mm-zswap-dont-return-lru_skip-if-we-have-dropped-lru-lock.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-zswap-dont-return-lru_skip-if-we-have-dropped-lru-lock.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Chengming Zhou <zhouchengming@bytedance.com>
Subject: mm/zswap: don't return LRU_SKIP if we have dropped lru lock
Date: Sun, 28 Jan 2024 13:28:49 +0000

Patch series "mm/zswap: fix race between lru writeback and swapoff", v2.

This series mainly fix the race problem between lru writeback and swapoff,
which is spotted by Yosry [1]. Please see the commits for details.

[1] https://lore.kernel.org/all/CAJD7tkasHsRnT_75-TXsEe58V9_OW6m3g6CF7Kmsvz8CKRG_EA@mail.gmail.com/


This patch (of 3):

LRU_SKIP can only be returned if we don't ever dropped lru lock, or we
need to return LRU_RETRY to restart from the head of lru list.

Otherwise, the iteration might continue from a cursor position that was
freed while the locks were dropped.

Actually we may need to introduce another LRU_STOP to really terminate the
ongoing shrinking scan process, when we encounter a warm page already in
the swap cache.  The current list_lru implementation doesn't have this
function to early break from __list_lru_walk_one.

Link: https://lkml.kernel.org/r/20240126-zswap-writeback-race-v2-1-b10479847099@bytedance.com
Fixes: b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure")
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Cc: Chris Li <chriscli@google.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/zswap.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/mm/zswap.c~mm-zswap-dont-return-lru_skip-if-we-have-dropped-lru-lock
+++ a/mm/zswap.c
@@ -901,10 +901,8 @@ static enum lru_status shrink_memcg_cb(s
 		 * into the warmer region. We should terminate shrinking (if we're in the dynamic
 		 * shrinker context).
 		 */
-		if (writeback_result == -EEXIST && encountered_page_in_swapcache) {
-			ret = LRU_SKIP;
+		if (writeback_result == -EEXIST && encountered_page_in_swapcache)
 			*encountered_page_in_swapcache = true;
-		}
 
 		goto put_unlock;
 	}
_

Patches currently in -mm which might be from zhouchengming@bytedance.com are

mm-zswap-make-sure-each-swapfile-always-have-zswap-rb-tree.patch
mm-zswap-split-zswap-rb-tree.patch
mm-zswap-dont-return-lru_skip-if-we-have-dropped-lru-lock.patch
mm-zswap-fix-race-between-lru-writeback-and-swapoff.patch
mm-list_lru-remove-list_lru_putback.patch