From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2AB194071F3 for ; Fri, 9 Oct 2026 05:58:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791525501; cv=none; b=b+FMyAZgmF9MmGJLfLja6DakBtFjy+ePp2d29eXH9mxaSw4WQ8Nt1F3UWor5eucqVHq1GtCi3ysByB/VxtWOYmgyn6azLTiP1Xw1NDDbNo9C1lKhUWvde2q+Q//+6Ni1pw6oeC4pbxBahVO/yHYgg5U7c1MtGzc1Nc6v0r7HbaQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791525501; c=relaxed/simple; bh=ZPF9wNCd627ItxjEkNzqJnepig/Hm/P21l95TnB4aTs=; h=Date:To:From:Subject:Message-Id; b=VUN7+t77CBizWRRLZwDFzCoWpdraBvcTaiLeS9iIy2iBs+FVDdzdPxDyX5aHQlYLjIfa4O8hsac3lOuXLgfnVsA6wIF78tiZf1K5zhtCm7o6y9spaph7mX2lPDMY/YJOtFkiUHCtqOZKLNdtMt2bESDy4RCKYyAH8sdOCQ3e9Uo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=ZaSZTCvq; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="ZaSZTCvq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0069E1F00893; Fri, 9 Oct 2026 05:58:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1791525500; bh=2dpf9bFxzihVxM7A617JQNmCy5cIqJ4IzwCpRUmVFtk=; h=Date:To:From:Subject; b=ZaSZTCvqcEmvFPYcV5yqt4aPnw3l2kSLwr4LIM7DXh5gefUhSm/A9R93aAeyz0WKg I/gOzWax3hWtMX82Z+QHQIxX3A+hEIL9YmbVNhHxpfVWIgH/FBo6ei7/Xc8G9ImK/m ZaeMrWqejMv0WrHF9lKR7ZD84+4JEj/Ln4ezh3dg= Date: Thu, 08 Oct 2026 22:58:19 -0700 To: mm-commits@vger.kernel.org,youngjun.park@lge.com,nphamcs@gmail.com,luizcap@redhat.com,kasong@tencent.com,chrisl@kernel.org,baoquan.he@linux.dev,baohua@kernel.org,shikemeng@huaweicloud.com,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] mm-swap-fix-potential-null-dereference-when-trying-a-sleep-table-allocation.patch removed from -mm tree Message-Id: <20261009055820.0069E1F00893@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm, swap: fix potential NULL dereference when trying a sleep table allocation has been removed from the -mm tree. Its filename was mm-swap-fix-potential-null-dereference-when-trying-a-sleep-table-allocation.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Kemeng Shi Subject: mm, swap: fix potential NULL dereference when trying a sleep table allocation Date: Mon, 7 Sep 2026 17:13:53 +0800 Patch series "mm, swap: some random fixes and cleanups", v3. This series contains some random fixes and cleanups. More details can be found in respective patches. This patch (of 4): The root cause of this issue is because multi-tables are updated in non atomic context. To be more specific, the issue could be triggerred as following: swap_alloc_fast swap_cluster_populate() /* Try a sleep allocation */ spin_unlock(&ci->lock); swap_cluster_alloc_table() rcu_assign_pointer(ci->table, table); ci = swap_cluster_lock(si, offset) cluster_is_usable(ci, order） if (!cluster_table_is_alloced(ci)) // ok alloc_swap_scan_cluster() cluster_scan_range() __swap_table_get() /* free table when more table allocation fails */ ci->memcg_table = kzalloc_obj(*ci->memcg_table, gfp); if (!ci->memcg_table) swap_cluster_free_table() rcu_assign_pointer(ci->table, NULL); table = rcu_dereference_check(ci->table, lockdep_is_held(&ci->lock)); atomic_long_read(&table[off]); // NULL dereference Since memory order guarantee between ci->table, as well as between ci->table and ci->zero_bitmap, fix the issue by making tables visible at the end of swap_cluster_populate(). Current memory order guarantee is as following: On write side: rcu_assign_pointer(ci->table, table) will offer release to ensure zero_bitmap and memcg_table visible before ci->table. On read side: folio_alloc_swap swap_alloc_fast/swap_alloc_slow /* ci->table: protected by cluster lock */ swap_cluster_lock cluster_is_usable ... __swap_table_set ... swap_cluster_unlock mem_cgroup_try_charge_swap ... /* memcg_table: protected by cluster lock */ swap_cluster_get_and_lock __swap_cgroup_set swap_cluster_unlock swap_writeout swap_zeromap_folio_set /* zero_bitmap: protected by cluster lock */ swap_cluster_get_and_lock __swap_table_set_zero swap_cluster_unlock Link: https://lore.kernel.org/20260907091356.53026-1-shikemeng@huaweicloud.com Link: https://lore.kernel.org/20260907091356.53026-2-shikemeng@huaweicloud.com Fixes: b197d41462c2 ("mm/memcg, swap: store cgroup id in cluster table directly") Signed-off-by: Kemeng Shi Signed-off-by: Andrew Morton Cc: Baoquan He Cc: Barry Song Cc: Chris Li Cc: Nhat Pham Cc: Kairui Song Cc: Luiz Capitulino Cc: Youngjun Park --- mm/swapfile.c | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) --- a/mm/swapfile.c~mm-swap-fix-potential-null-dereference-when-trying-a-sleep-table-allocation +++ a/mm/swapfile.c @@ -416,6 +416,17 @@ static void swap_cluster_free_table_foli folio_put(folio); } +static void swap_cluster_free_count_table(struct swap_table *table) +{ + if (!SWP_TABLE_USE_PAGE) { + kmem_cache_free(swap_table_cachep, table); + return; + } + + call_rcu(&(folio_page(virt_to_folio(table), 0)->rcu_head), + swap_cluster_free_table_folio_rcu_cb); +} + static void swap_cluster_free_table(struct swap_cluster_info *ci) { struct swap_table *table; @@ -435,13 +446,7 @@ static void swap_cluster_free_table(stru return; rcu_assign_pointer(ci->table, NULL); - if (!SWP_TABLE_USE_PAGE) { - kmem_cache_free(swap_table_cachep, table); - return; - } - - call_rcu(&(folio_page(virt_to_folio(table), 0)->rcu_head), - swap_cluster_free_table_folio_rcu_cb); + swap_cluster_free_count_table(table); } static int swap_cluster_alloc_table(struct swap_cluster_info *ci, gfp_t gfp) @@ -464,14 +469,12 @@ static int swap_cluster_alloc_table(stru if (!table) return -ENOMEM; - rcu_assign_pointer(ci->table, table); - #ifdef CONFIG_MEMCG if (!mem_cgroup_disabled()) { VM_WARN_ON_ONCE(ci->memcg_table); ci->memcg_table = kzalloc_obj(*ci->memcg_table, gfp); if (!ci->memcg_table) { - swap_cluster_free_table(ci); + swap_cluster_free_count_table(table); return -ENOMEM; } } @@ -482,9 +485,16 @@ static int swap_cluster_alloc_table(stru ci->zero_bitmap = bitmap_zalloc(SWAPFILE_CLUSTER, gfp); if (!ci->zero_bitmap) { swap_cluster_free_table(ci); + swap_cluster_free_count_table(table); return -ENOMEM; } #endif + + /* + * Make tables visible to cluster_is_usable() after everything is + * ready. + */ + rcu_assign_pointer(ci->table, table); return 0; } _ Patches currently in -mm which might be from shikemeng@huaweicloud.com are