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AJvYcCVNlDxpDR1Fqq7HS609SUDRCMVkMZdSfU1OZu6VzaKZwzowtvTTLqq1pPksHQ1lWU+uB5BUPdAYYQ==@kvack.org X-Gm-Message-State: AOJu0Yy8SagiaFBgD+y/bw3m7zltsERDiKURjypR2Ki2zaXfJnWEgg+Y 3tGFrfWKRom2KoDtpG5FKsJSjrYhJBzv4DRygcsVGfZmGGozHmjn5HOdFPvHcvfyBA/JBwYRblP zDjEge8M0gpt/wiX/cw== X-Google-Smtp-Source: AGHT+IHO+KIS6IWsnU8P0JcAlrA8VQx6zkqU6P2LdNHDD4x04qVDshzzX7V4PSbQjsjSWgp/VwS4Rbtz7I+owiPA X-Received: from pjbph15.prod.google.com ([2002:a17:90b:3bcf:b0:2ea:4139:e72d]) (user=yosryahmed job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:e18c:b0:2ee:b2be:f398 with SMTP id 98e67ed59e1d1-2f548f09f04mr802536a91.2.1736288559332; Tue, 07 Jan 2025 14:22:39 -0800 (PST) Date: Tue, 7 Jan 2025 22:22:34 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.47.1.613.gc27f4b7a9f-goog Message-ID: <20250107222236.2715883-1-yosryahmed@google.com> Subject: [PATCH v2 1/2] Revert "mm: zswap: fix race between [de]compression and CPU hotunplug" From: Yosry Ahmed To: Andrew Morton Cc: Johannes Weiner , Nhat Pham , Chengming Zhou , Vitaly Wool , Barry Song , Sam Sun , Kanchana P Sridhar , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yosry Ahmed , syzbot X-Rspamd-Queue-Id: 9733D18000E X-Stat-Signature: az8rq1fjeru5547prrzycuawhezprbmo X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1736288560-358888 X-HE-Meta: U2FsdGVkX1+MX3LwEH7L4XFGDLBwppW7RuZ2cNfVJPQKzwC92C0u/B/6f2ASe7KFQJrd9BOSkQTDR6uZyPk6yftVgC38Sx4QJu0T+pRFUrnyhX3M5F5XVfCLBtixleayIwc0LBJFhj/fdcLmLhuIHwaXFthijWfH636A18ksk5gb8Ba9m/5MR0r7QDUjkUtNChteNE1u1aXFjfVYpbcJVVJSiL+RK8G8HNKKdxMLNQRATZRP7l9F7yc1JCuTNxxUv4enpwruooPlAL46fRkVWTCH696gJY3Fv5FEbsOJ8rdMhfa2LHeksuc9y8RrLLUuP1/tWlLTRNLm4W2tfbdieElF9u0ERDOYru0Nsavjx3HBP6GDRrUvngskAGYxbF3wFLtkZ11vlt+Th/mn8d5zw5dhBo42ntCl7Weiq4iw+7g4JP8VSd8Q3USj2TJ/gYwNCvfXuvPGeb/wPfWNVlSf0UlAgJlOhr6SsRQF/IrVKtPobmlZBKCgTO6cuWhWN7oRU2sMnaOpBUfXltQe0GbDoVR27sWLrCWLT02FY6DsARABoU6IxL68CgojLHorioQYXmfxXgAgvG6TNWw6TXXLYhCowMJWuomXgvRUF2pXCSdREgzvaECKMx6D9naB+wSrblmb/fv87Bcy/IdwvrRQ63RN+1Ljoe3mjJ4qO4Hp5RW5E6JC7gui+/x5NoXs/g6j4XJwKeUIE402JWDIWp5I9wcGXM7u/mgshV7CSlheib5eqYwvmKXYpz18gPjPZ6nbJGZmcm+sdg+EcQSxYikDX9cjOJBPknJJqPTEEFeRI7JrLE/768+Vj+rzN2mDc1U1e4wZbBpT9l0BuHzOHJpbG8J/RgxzmWUaj0hU18EB9GJMAfrmSa43lLhld7vhFevir5PCZiWu/8GOfWnlGOVy08/p8d2j9tZ7JU7aOadOr+1yM9VLO2wd+clWXxcclJgABeHc9J2DmW5UcQzcvEy R6JUGale 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: This reverts commit eaebeb93922ca6ab0dd92027b73d0112701706ef. Commit eaebeb93922c ("mm: zswap: fix race between [de]compression and CPU hotunplug") used the CPU hotplug lock in zswap compress/decompress operations to protect against a race with CPU hotunplug making some per-CPU resources go away. However, zswap compress/decompress can be reached through reclaim while the lock is held, resulting in a potential deadlock as reported by syzbot: ====================================================== WARNING: possible circular locking dependency detected 6.13.0-rc6-syzkaller-00006-g5428dc1906dd #0 Not tainted ------------------------------------------------------ kswapd0/89 is trying to acquire lock: ffffffff8e7d2ed0 (cpu_hotplug_lock){++++}-{0:0}, at: acomp_ctx_get_cpu mm/zswap.c:886 [inline] ffffffff8e7d2ed0 (cpu_hotplug_lock){++++}-{0:0}, at: zswap_compress mm/zswap.c:908 [inline] ffffffff8e7d2ed0 (cpu_hotplug_lock){++++}-{0:0}, at: zswap_store_page mm/zswap.c:1439 [inline] ffffffff8e7d2ed0 (cpu_hotplug_lock){++++}-{0:0}, at: zswap_store+0xa74/0x1ba0 mm/zswap.c:1546 but task is already holding lock: ffffffff8ea355a0 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:6871 [inline] ffffffff8ea355a0 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0xb58/0x2f30 mm/vmscan.c:7253 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (fs_reclaim){+.+.}-{0:0}: lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849 __fs_reclaim_acquire mm/page_alloc.c:3853 [inline] fs_reclaim_acquire+0x88/0x130 mm/page_alloc.c:3867 might_alloc include/linux/sched/mm.h:318 [inline] slab_pre_alloc_hook mm/slub.c:4070 [inline] slab_alloc_node mm/slub.c:4148 [inline] __kmalloc_cache_node_noprof+0x40/0x3a0 mm/slub.c:4337 kmalloc_node_noprof include/linux/slab.h:924 [inline] alloc_worker kernel/workqueue.c:2638 [inline] create_worker+0x11b/0x720 kernel/workqueue.c:2781 workqueue_prepare_cpu+0xe3/0x170 kernel/workqueue.c:6628 cpuhp_invoke_callback+0x48d/0x830 kernel/cpu.c:194 __cpuhp_invoke_callback_range kernel/cpu.c:965 [inline] cpuhp_invoke_callback_range kernel/cpu.c:989 [inline] cpuhp_up_callbacks kernel/cpu.c:1020 [inline] _cpu_up+0x2b3/0x580 kernel/cpu.c:1690 cpu_up+0x184/0x230 kernel/cpu.c:1722 cpuhp_bringup_mask+0xdf/0x260 kernel/cpu.c:1788 cpuhp_bringup_cpus_parallel+0xf9/0x160 kernel/cpu.c:1878 bringup_nonboot_cpus+0x2b/0x50 kernel/cpu.c:1892 smp_init+0x34/0x150 kernel/smp.c:1009 kernel_init_freeable+0x417/0x5d0 init/main.c:1569 kernel_init+0x1d/0x2b0 init/main.c:1466 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 -> #0 (cpu_hotplug_lock){++++}-{0:0}: check_prev_add kernel/locking/lockdep.c:3161 [inline] check_prevs_add kernel/locking/lockdep.c:3280 [inline] validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5226 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849 percpu_down_read include/linux/percpu-rwsem.h:51 [inline] cpus_read_lock+0x42/0x150 kernel/cpu.c:490 acomp_ctx_get_cpu mm/zswap.c:886 [inline] zswap_compress mm/zswap.c:908 [inline] zswap_store_page mm/zswap.c:1439 [inline] zswap_store+0xa74/0x1ba0 mm/zswap.c:1546 swap_writepage+0x647/0xce0 mm/page_io.c:279 shmem_writepage+0x1248/0x1610 mm/shmem.c:1579 pageout mm/vmscan.c:696 [inline] shrink_folio_list+0x35ee/0x57e0 mm/vmscan.c:1374 shrink_inactive_list mm/vmscan.c:1967 [inline] shrink_list mm/vmscan.c:2205 [inline] shrink_lruvec+0x16db/0x2f30 mm/vmscan.c:5734 mem_cgroup_shrink_node+0x385/0x8e0 mm/vmscan.c:6575 mem_cgroup_soft_reclaim mm/memcontrol-v1.c:312 [inline] memcg1_soft_limit_reclaim+0x346/0x810 mm/memcontrol-v1.c:362 balance_pgdat mm/vmscan.c:6975 [inline] kswapd+0x17b3/0x2f30 mm/vmscan.c:7253 kthread+0x2f0/0x390 kernel/kthread.c:389 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(fs_reclaim); lock(cpu_hotplug_lock); lock(fs_reclaim); rlock(cpu_hotplug_lock); *** DEADLOCK *** 1 lock held by kswapd0/89: #0: ffffffff8ea355a0 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:6871 [inline] #0: ffffffff8ea355a0 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0xb58/0x2f30 mm/vmscan.c:7253 stack backtrace: CPU: 0 UID: 0 PID: 89 Comm: kswapd0 Not tainted 6.13.0-rc6-syzkaller-00006-g5428dc1906dd #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120 print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2074 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2206 check_prev_add kernel/locking/lockdep.c:3161 [inline] check_prevs_add kernel/locking/lockdep.c:3280 [inline] validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5226 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849 percpu_down_read include/linux/percpu-rwsem.h:51 [inline] cpus_read_lock+0x42/0x150 kernel/cpu.c:490 acomp_ctx_get_cpu mm/zswap.c:886 [inline] zswap_compress mm/zswap.c:908 [inline] zswap_store_page mm/zswap.c:1439 [inline] zswap_store+0xa74/0x1ba0 mm/zswap.c:1546 swap_writepage+0x647/0xce0 mm/page_io.c:279 shmem_writepage+0x1248/0x1610 mm/shmem.c:1579 pageout mm/vmscan.c:696 [inline] shrink_folio_list+0x35ee/0x57e0 mm/vmscan.c:1374 shrink_inactive_list mm/vmscan.c:1967 [inline] shrink_list mm/vmscan.c:2205 [inline] shrink_lruvec+0x16db/0x2f30 mm/vmscan.c:5734 mem_cgroup_shrink_node+0x385/0x8e0 mm/vmscan.c:6575 mem_cgroup_soft_reclaim mm/memcontrol-v1.c:312 [inline] memcg1_soft_limit_reclaim+0x346/0x810 mm/memcontrol-v1.c:362 balance_pgdat mm/vmscan.c:6975 [inline] kswapd+0x17b3/0x2f30 mm/vmscan.c:7253 kthread+0x2f0/0x390 kernel/kthread.c:389 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 Revert the change. A different fix for the race with CPU hotunplug will follow. Reported-by: syzbot Signed-off-by: Yosry Ahmed --- The patches apply on top of mm-hotfixes-unstable and are meant for v6.13. Andrew, I am not sure what's the best way to handle this. This fix is already merged into Linus's tree and had CC:stable, so I thought it's best to revert it and replace it with a separate fix that would be easy to backport instead of the revert patch, especially that functionally the new fix is different anyway. v1 -> v2: - Disable migration as an alternative fix instead of SRCU, and explain why SRCU and cpus_read_lock() cannot be used in the commit log of patch 2. --- mm/zswap.c | 19 +++---------------- 1 file changed, 3 insertions(+), 16 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index 5a27af8d86ea9..f6316b66fb236 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -880,18 +880,6 @@ static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node) return 0; } -/* Prevent CPU hotplug from freeing up the per-CPU acomp_ctx resources */ -static struct crypto_acomp_ctx *acomp_ctx_get_cpu(struct crypto_acomp_ctx __percpu *acomp_ctx) -{ - cpus_read_lock(); - return raw_cpu_ptr(acomp_ctx); -} - -static void acomp_ctx_put_cpu(void) -{ - cpus_read_unlock(); -} - static bool zswap_compress(struct page *page, struct zswap_entry *entry, struct zswap_pool *pool) { @@ -905,7 +893,8 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry, gfp_t gfp; u8 *dst; - acomp_ctx = acomp_ctx_get_cpu(pool->acomp_ctx); + acomp_ctx = raw_cpu_ptr(pool->acomp_ctx); + mutex_lock(&acomp_ctx->mutex); dst = acomp_ctx->buffer; @@ -961,7 +950,6 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry, zswap_reject_alloc_fail++; mutex_unlock(&acomp_ctx->mutex); - acomp_ctx_put_cpu(); return comp_ret == 0 && alloc_ret == 0; } @@ -972,7 +960,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio) struct crypto_acomp_ctx *acomp_ctx; u8 *src; - acomp_ctx = acomp_ctx_get_cpu(entry->pool->acomp_ctx); + acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx); mutex_lock(&acomp_ctx->mutex); src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO); @@ -1002,7 +990,6 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio) if (src != acomp_ctx->buffer) zpool_unmap_handle(zpool, entry->handle); - acomp_ctx_put_cpu(); } /*********************************