+ zsmalloc-reset-compaction-source-zspage-pointer-after-putback_zspage.patch added to mm-unstable branch

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

The patch titled
     Subject: zsmalloc: reset compaction source zspage pointer after putback_zspage()
has been added to the -mm mm-unstable branch.  Its filename is
     zsmalloc-reset-compaction-source-zspage-pointer-after-putback_zspage.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zsmalloc-reset-compaction-source-zspage-pointer-after-putback_zspage.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: Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: zsmalloc: reset compaction source zspage pointer after putback_zspage()
Date: Mon, 17 Apr 2023 22:08:50 +0900

The current implementation of the compaction loop fails to set the source
zspage pointer to NULL in all cases, leading to a potential issue where
__zs_compact() could use a stale zspage pointer.  This pointer could even
point to a previously freed zspage, causing unexpected behavior in the
putback_zspage() and migrate_write_unlock() functions after returning from
the compaction loop.

Address the issue by ensuring that the source zspage pointer is always set
to NULL when it should be.

Link: https://lkml.kernel.org/r/20230417130850.1784777-1-senozhatsky@chromium.org
Fixes: 5a845e9f2d66 ("zsmalloc: rework compaction algorithm")
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reported-by: Yu Zhao <yuzhao@google.com>
Tested-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/zsmalloc.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/zsmalloc.c~zsmalloc-reset-compaction-source-zspage-pointer-after-putback_zspage
+++ a/mm/zsmalloc.c
@@ -2239,8 +2239,8 @@ static unsigned long __zs_compact(struct
 		if (fg == ZS_INUSE_RATIO_0) {
 			free_zspage(pool, class, src_zspage);
 			pages_freed += class->pages_per_zspage;
-			src_zspage = NULL;
 		}
+		src_zspage = NULL;
 
 		if (get_fullness_group(class, dst_zspage) == ZS_INUSE_RATIO_100
 		    || spin_is_contended(&pool->lock)) {
_

Patches currently in -mm which might be from senozhatsky@chromium.org are

zsmalloc-reset-compaction-source-zspage-pointer-after-putback_zspage.patch