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AJvYcCXPz9JH/NoXA7GtjiGxim8PmyrzZdYSHE4DVBqdGRujoVu+ge7sSq0QMZS5Y/BXDdkFPP14Xog74A==@kvack.org X-Gm-Message-State: AOJu0YzdogF+Rp85hbeA6ScXoq2+xxAV198CRpjEQAfsPBLFKwaZ3tKP a7CHsADcM1I0HZJkQJoXJHpQYYz+UiT3Vy1/epRlerWuEF+AC1cTbNimX4/Y6a4PB0H2+yiNOii 2teV0JiSY1bAOMMuKhg== X-Google-Smtp-Source: AGHT+IHjijLOYp4AUNoDGD4jWaY1kQTGhUKSCw5g1bV4hH4sMyOFTHYanZ0otpFePXew3dGKIXSVbgDdI2BXiXru X-Received: from pghe6.prod.google.com ([2002:a63:e006:0:b0:910:1db1:4ba]) (user=yosryahmed job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:d499:b0:1d9:c615:d1e6 with SMTP id adf61e73a8af0-1e5dfb65989mr82982587637.0.1736207573212; Mon, 06 Jan 2025 15:52:53 -0800 (PST) Date: Mon, 6 Jan 2025 23:52:47 +0000 In-Reply-To: <20250106235248.1501064-1-yosryahmed@google.com> Mime-Version: 1.0 References: <20250106235248.1501064-1-yosryahmed@google.com> X-Mailer: git-send-email 2.47.1.613.gc27f4b7a9f-goog Message-ID: <20250106235248.1501064-2-yosryahmed@google.com> Subject: [PATCH 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 , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yosry Ahmed , syzbot X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 8657A40003 X-Rspam-User: X-Stat-Signature: simsngspn9xj336ricre6xaaztozs41d X-HE-Tag: 1736207574-313961 X-HE-Meta: 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 dffk/JhT 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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 --- 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, especially that functionally the new fix is completely different anyway. Does the revert automatically signal the stable maintainers to drop it? Do we need to add CC:stable to this revert as well? --- 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(); } /*********************************