From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 23CE9C7EE22 for ; Wed, 17 May 2023 22:25:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229519AbjEQWZV (ORCPT ); Wed, 17 May 2023 18:25:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229461AbjEQWZU (ORCPT ); Wed, 17 May 2023 18:25:20 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16FE41B5; Wed, 17 May 2023 15:25:19 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 8BD9163DB5; Wed, 17 May 2023 22:25:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D526EC433EF; Wed, 17 May 2023 22:25:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1684362318; bh=fTKg1JDzTcT8Kh89vLowrOxLncRczAXcjF7Q4Jsmvyg=; h=Date:To:From:Subject:From; b=jNDo2Nlyvv+jwxWP0UJSpxrQPKyJSHEsYImDwxVO9aLOoQ0Hxiy3RmH6XfGhF7b9b Y5O7iwS+rpm92BeuKFAE9aYEakmXM9R1TxDBKm4xFIha3dFE6J/+j5C3SGHIZDHsEp FDr/CY3cABglxaCTR1wktjWOAK51zGOEsCGs72Mo= Date: Wed, 17 May 2023 15:25:17 -0700 To: mm-commits@vger.kernel.org, vitaly.wool@konsulko.com, stable@vger.kernel.org, sjenning@redhat.com, senozhatsky@chromium.org, ngupta@vflare.org, minchan@kernel.org, hannes@cmpxchg.org, ddstreet@ieee.org, nphamcs@gmail.com, akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] zsmalloc-move-lru-update-from-zs_map_object-to-zs_malloc.patch removed from -mm tree Message-Id: <20230517222517.D526EC433EF@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The quilt patch titled Subject: zsmalloc: move LRU update from zs_map_object() to zs_malloc() has been removed from the -mm tree. Its filename was zsmalloc-move-lru-update-from-zs_map_object-to-zs_malloc.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: Nhat Pham Subject: zsmalloc: move LRU update from zs_map_object() to zs_malloc() Date: Fri, 5 May 2023 11:50:54 -0700 Under memory pressure, we sometimes observe the following crash: [ 5694.832838] ------------[ cut here ]------------ [ 5694.842093] list_del corruption, ffff888014b6a448->next is LIST_POISON1 (dead000000000100) [ 5694.858677] WARNING: CPU: 33 PID: 418824 at lib/list_debug.c:47 __list_del_entry_valid+0x42/0x80 [ 5694.961820] CPU: 33 PID: 418824 Comm: fuse_counters.s Kdump: loaded Tainted: G S 5.19.0-0_fbk3_rc3_hoangnhatpzsdynshrv41_10870_g85a9558a25de #1 [ 5694.990194] Hardware name: Wiwynn Twin Lakes MP/Twin Lakes Passive MP, BIOS YMM16 05/24/2021 [ 5695.007072] RIP: 0010:__list_del_entry_valid+0x42/0x80 [ 5695.017351] Code: 08 48 83 c2 22 48 39 d0 74 24 48 8b 10 48 39 f2 75 2c 48 8b 51 08 b0 01 48 39 f2 75 34 c3 48 c7 c7 55 d7 78 82 e8 4e 45 3b 00 <0f> 0b eb 31 48 c7 c7 27 a8 70 82 e8 3e 45 3b 00 0f 0b eb 21 48 c7 [ 5695.054919] RSP: 0018:ffffc90027aef4f0 EFLAGS: 00010246 [ 5695.065366] RAX: 41fe484987275300 RBX: ffff888008988180 RCX: 0000000000000000 [ 5695.079636] RDX: ffff88886006c280 RSI: ffff888860060480 RDI: ffff888860060480 [ 5695.093904] RBP: 0000000000000002 R08: 0000000000000000 R09: ffffc90027aef370 [ 5695.108175] R10: 0000000000000000 R11: ffffffff82fdf1c0 R12: 0000000010000002 [ 5695.122447] R13: ffff888014b6a448 R14: ffff888014b6a420 R15: 00000000138dc240 [ 5695.136717] FS: 00007f23a7d3f740(0000) GS:ffff888860040000(0000) knlGS:0000000000000000 [ 5695.152899] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 5695.164388] CR2: 0000560ceaab6ac0 CR3: 000000001c06c001 CR4: 00000000007706e0 [ 5695.178659] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 5695.192927] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 5695.207197] PKRU: 55555554 [ 5695.212602] Call Trace: [ 5695.217486] [ 5695.221674] zs_map_object+0x91/0x270 [ 5695.229000] zswap_frontswap_store+0x33d/0x870 [ 5695.237885] ? do_raw_spin_lock+0x5d/0xa0 [ 5695.245899] __frontswap_store+0x51/0xb0 [ 5695.253742] swap_writepage+0x3c/0x60 [ 5695.261063] shrink_page_list+0x738/0x1230 [ 5695.269255] shrink_lruvec+0x5ec/0xcd0 [ 5695.276749] ? shrink_slab+0x187/0x5f0 [ 5695.284240] ? mem_cgroup_iter+0x6e/0x120 [ 5695.292255] shrink_node+0x293/0x7b0 [ 5695.299402] do_try_to_free_pages+0xea/0x550 [ 5695.307940] try_to_free_pages+0x19a/0x490 [ 5695.316126] __folio_alloc+0x19ff/0x3e40 [ 5695.323971] ? __filemap_get_folio+0x8a/0x4e0 [ 5695.332681] ? walk_component+0x2a8/0xb50 [ 5695.340697] ? generic_permission+0xda/0x2a0 [ 5695.349231] ? __filemap_get_folio+0x8a/0x4e0 [ 5695.357940] ? walk_component+0x2a8/0xb50 [ 5695.365955] vma_alloc_folio+0x10e/0x570 [ 5695.373796] ? walk_component+0x52/0xb50 [ 5695.381634] wp_page_copy+0x38c/0xc10 [ 5695.388953] ? filename_lookup+0x378/0xbc0 [ 5695.397140] handle_mm_fault+0x87f/0x1800 [ 5695.405157] do_user_addr_fault+0x1bd/0x570 [ 5695.413520] exc_page_fault+0x5d/0x110 [ 5695.421017] asm_exc_page_fault+0x22/0x30 After some investigation, I have found the following issue: unlike other zswap backends, zsmalloc performs the LRU list update at the object mapping time, rather than when the slot for the object is allocated. This deviation was discussed and agreed upon during the review process of the zsmalloc writeback patch series: https://lore.kernel.org/lkml/Y3flcAXNxxrvy3ZH@cmpxchg.org/ Unfortunately, this introduces a subtle bug that occurs when there is a concurrent store and reclaim, which interleave as follows: zswap_frontswap_store() shrink_worker() zs_malloc() zs_zpool_shrink() spin_lock(&pool->lock) zs_reclaim_page() zspage = find_get_zspage() spin_unlock(&pool->lock) spin_lock(&pool->lock) zspage = list_first_entry(&pool->lru) list_del(&zspage->lru) zspage->lru.next = LIST_POISON1 zspage->lru.prev = LIST_POISON2 spin_unlock(&pool->lock) zs_map_object() spin_lock(&pool->lock) if (!list_empty(&zspage->lru)) list_del(&zspage->lru) CHECK_DATA_CORRUPTION(next == LIST_POISON1) /* BOOM */ With the current upstream code, this issue rarely happens. zswap only triggers writeback when the pool is already full, at which point all further store attempts are short-circuited. This creates an implicit pseudo-serialization between reclaim and store. I am working on a new zswap shrinking mechanism, which makes interleaving reclaim and store more likely, exposing this bug. zbud and z3fold do not have this problem, because they perform the LRU list update in the alloc function, while still holding the pool's lock. This patch fixes the aforementioned bug by moving the LRU update back to zs_malloc(), analogous to zbud and z3fold. Link: https://lkml.kernel.org/r/20230505185054.2417128-1-nphamcs@gmail.com Fixes: 64f768c6b32e ("zsmalloc: add a LRU to zs_pool to keep track of zspages in LRU order") Signed-off-by: Nhat Pham Suggested-by: Johannes Weiner Acked-by: Johannes Weiner Reviewed-by: Sergey Senozhatsky Acked-by: Minchan Kim Cc: Dan Streetman Cc: Nitin Gupta Cc: Seth Jennings Cc: Vitaly Wool Cc: Signed-off-by: Andrew Morton --- mm/zsmalloc.c | 36 +++++++++--------------------------- 1 file changed, 9 insertions(+), 27 deletions(-) --- a/mm/zsmalloc.c~zsmalloc-move-lru-update-from-zs_map_object-to-zs_malloc +++ a/mm/zsmalloc.c @@ -1331,31 +1331,6 @@ void *zs_map_object(struct zs_pool *pool obj_to_location(obj, &page, &obj_idx); zspage = get_zspage(page); -#ifdef CONFIG_ZPOOL - /* - * Move the zspage to front of pool's LRU. - * - * Note that this is swap-specific, so by definition there are no ongoing - * accesses to the memory while the page is swapped out that would make - * it "hot". A new entry is hot, then ages to the tail until it gets either - * written back or swaps back in. - * - * Furthermore, map is also called during writeback. We must not put an - * isolated page on the LRU mid-reclaim. - * - * As a result, only update the LRU when the page is mapped for write - * when it's first instantiated. - * - * This is a deviation from the other backends, which perform this update - * in the allocation function (zbud_alloc, z3fold_alloc). - */ - if (mm == ZS_MM_WO) { - if (!list_empty(&zspage->lru)) - list_del(&zspage->lru); - list_add(&zspage->lru, &pool->lru); - } -#endif - /* * migration cannot move any zpages in this zspage. Here, pool->lock * is too heavy since callers would take some time until they calls @@ -1525,9 +1500,8 @@ unsigned long zs_malloc(struct zs_pool * fix_fullness_group(class, zspage); record_obj(handle, obj); class_stat_inc(class, ZS_OBJS_INUSE, 1); - spin_unlock(&pool->lock); - return handle; + goto out; } spin_unlock(&pool->lock); @@ -1550,6 +1524,14 @@ unsigned long zs_malloc(struct zs_pool * /* We completely set up zspage so mark them as movable */ SetZsPageMovable(pool, zspage); +out: +#ifdef CONFIG_ZPOOL + /* Add/move zspage to beginning of LRU */ + if (!list_empty(&zspage->lru)) + list_del(&zspage->lru); + list_add(&zspage->lru, &pool->lru); +#endif + spin_unlock(&pool->lock); return handle; _ Patches currently in -mm which might be from nphamcs@gmail.com are workingset-refactor-lru-refault-to-expose-refault-recency-check.patch cachestat-implement-cachestat-syscall.patch cachestat-implement-cachestat-syscall-fix.patch cachestat-wire-up-cachestat-for-other-architectures.patch cachestat-wire-up-cachestat-for-other-architectures-fix.patch selftests-add-selftests-for-cachestat.patch