[merged mm-hotfixes-stable] zsmalloc-fix-races-between-modifications-of-fullness-and-isolated.patch removed from -mm tree

[merged mm-hotfixes-stable] zsmalloc-fix-races-between-modifications-of-fullness-and-isolated.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: zsmalloc: fix races between modifications of fullness and isolated
has been removed from the -mm tree.  Its filename was
     zsmalloc-fix-races-between-modifications-of-fullness-and-isolated.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Andrew Yang <andrew.yang@mediatek.com>
Subject: zsmalloc: fix races between modifications of fullness and isolated
Date: Fri, 21 Jul 2023 14:37:01 +0800

We encountered many kernel exceptions of VM_BUG_ON(zspage->isolated ==
0) in dec_zspage_isolation() and BUG_ON(!pages[1]) in zs_unmap_object()
lately.  This issue only occurs when migration and reclamation occur at
the same time.

With our memory stress test, we can reproduce this issue several times
a day.  We have no idea why no one else encountered this issue.  BTW,
we switched to the new kernel version with this defect a few months
ago.

Since fullness and isolated share the same unsigned int, modifications of
them should be protected by the same lock.

[andrew.yang@mediatek.com: move comment]
  Link: https://lkml.kernel.org/r/20230727062910.6337-1-andrew.yang@mediatek.com
Link: https://lkml.kernel.org/r/20230721063705.11455-1-andrew.yang@mediatek.com
Fixes: c4549b871102 ("zsmalloc: remove zspage isolation for migration")
Signed-off-by: Andrew Yang <andrew.yang@mediatek.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/zsmalloc.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

--- a/mm/zsmalloc.c~zsmalloc-fix-races-between-modifications-of-fullness-and-isolated
+++ a/mm/zsmalloc.c
@@ -1798,6 +1798,7 @@ static void replace_sub_page(struct size
 
 static bool zs_page_isolate(struct page *page, isolate_mode_t mode)
 {
+	struct zs_pool *pool;
 	struct zspage *zspage;
 
 	/*
@@ -1807,9 +1808,10 @@ static bool zs_page_isolate(struct page
 	VM_BUG_ON_PAGE(PageIsolated(page), page);
 
 	zspage = get_zspage(page);
-	migrate_write_lock(zspage);
+	pool = zspage->pool;
+	spin_lock(&pool->lock);
 	inc_zspage_isolation(zspage);
-	migrate_write_unlock(zspage);
+	spin_unlock(&pool->lock);
 
 	return true;
 }
@@ -1875,12 +1877,12 @@ static int zs_page_migrate(struct page *
 	kunmap_atomic(s_addr);
 
 	replace_sub_page(class, zspage, newpage, page);
+	dec_zspage_isolation(zspage);
 	/*
 	 * Since we complete the data copy and set up new zspage structure,
 	 * it's okay to release the pool's lock.
 	 */
 	spin_unlock(&pool->lock);
-	dec_zspage_isolation(zspage);
 	migrate_write_unlock(zspage);
 
 	get_page(newpage);
@@ -1897,14 +1899,16 @@ static int zs_page_migrate(struct page *
 
 static void zs_page_putback(struct page *page)
 {
+	struct zs_pool *pool;
 	struct zspage *zspage;
 
 	VM_BUG_ON_PAGE(!PageIsolated(page), page);
 
 	zspage = get_zspage(page);
-	migrate_write_lock(zspage);
+	pool = zspage->pool;
+	spin_lock(&pool->lock);
 	dec_zspage_isolation(zspage);
-	migrate_write_unlock(zspage);
+	spin_unlock(&pool->lock);
 }
 
 static const struct movable_operations zsmalloc_mops = {
_

Patches currently in -mm which might be from andrew.yang@mediatek.com are

fs-drop_caches-draining-pages-before-dropping-caches.patch