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AJvYcCU8Wp5kvSneNfyXvjTW3AtA30I6wtmGpDCoSUIWebtRRV+oEGVobrnAKGLo9NIOzPNNHyEU8+8Y5A==@kvack.org X-Gm-Message-State: AOJu0YyfXb1rLK+6jHBjSKj9UIsBF9w0vO6oLq4ZwpHPQGewKr/T0Iyk 30wPaHBZLrb1CBOoQk/RvYDXfPaoBfyzJ7zPlk884yZGedmXHtHiGx6Ldd8wY+tj685tNDHvgD2 reZhqt6sdga2bbRgdSQpAZn/WPq5wic1Xzs0e X-Gm-Gg: ASbGncv5AWCyQagH7oCFAcnLG1apx69OnsdHJi0/xDyRRFVRIfZiFbbg+YJ+412MgQJ NvSPVEPAcAx2HP8D+DPOmG9HkXKIP+8BTcXw= X-Google-Smtp-Source: AGHT+IFD1KWSlrqLaE+gVjFH9vuie41Y4x3Bgx9nfPQVgnHndKmDnr1GTcHyKTXTrA0LsMyo4jRz0lXs9gxJj6Tgx4o= X-Received: by 2002:a05:6214:daf:b0:6d8:b3a7:75af with SMTP id 6a1803df08f44-6df9b2d8dd6mr26152236d6.46.1736321088941; Tue, 07 Jan 2025 23:24:48 -0800 (PST) MIME-Version: 1.0 References: <20250107074724.1756696-1-yosryahmed@google.com> <20250107074724.1756696-2-yosryahmed@google.com> <20250107180345.GD37530@cmpxchg.org> <20250107224225.ca41ec2f0340b6b768f44a6a@linux-foundation.org> In-Reply-To: <20250107224225.ca41ec2f0340b6b768f44a6a@linux-foundation.org> From: Yosry Ahmed Date: Tue, 7 Jan 2025 23:24:12 -0800 X-Gm-Features: AbW1kvZ_lyoJRdFO0iZF3jcIgxnxWRXD8WgPZDEF8--ksKwm0V_ZBG_y8dUr-nI Message-ID: Subject: Re: [PATCH RESEND 2/2] mm: zswap: use SRCU to synchronize with CPU hotunplug To: Andrew Morton Cc: Nhat Pham , Johannes Weiner , Chengming Zhou , Vitaly Wool , Barry Song , Sam Sun , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 1C8E340006 X-Stat-Signature: 6qb43gudx7wdp8pjg3hnf4dqidp9c4zu X-Rspam-User: X-HE-Tag: 1736321089-843022 X-HE-Meta: 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 dyY/bORZ RdOc3iJJwD7eoPgXCVIYZrjrt1dk1A90PsWZkT8e7xXEVFgwHFxLgku6WMmsP02TXZdqR50WOSMcwKtiE3n5/YJkcsKIRb5TCQp8vZUYZqQ3QF5IUmxdCEY1+TaxkEN9BtadH7J50mNt10r2JiHXqARvrovSwpzq5X2r22g0V7p+9nPDfD4pO/JjHARsvH0K1zr5z7Z/aqfYA6ACBvn/8DP5XQg68ZESaglSz9x6xTZr19S6+LfBjWBPvbZ91KSlzOlcqOT2fEPiqILOLte3D/STPMwBOlXrMJ4e+1rwNPDgmleiGgtdf6jQewrZmec+QA+kvKTlwZ11tbAgdNz6OzhOim2G9K1cPebswR4O/fhokG6ODTsj23s0rY+FISifSgBne0VCNa1kxT+t46U/2NfXD6/mH6ZRLjs3Vvt+6jkt/99TK4eCsLijWoEmp932D4L41+ts9SSM9bFtqIjbT4HHxSQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jan 7, 2025 at 10:42=E2=80=AFPM Andrew Morton wrote: > > > > > Andrew, could you please pick up patch 1 (the revert) while we figure > > out the alternative fix? It's important that it lands in v6.13 to > > avoid the possibility of deadlock. Figuring out an alternative fix is > > less important. > > I have the below patch in mm-hotfixes-unstable. Please only keep that patch, "Revert "mm: zswap: fix race between [de]compression and CPU hotunplug", in mm-hotfixes-unstable. > > I also have > https://lkml.kernel.org/r/20250107222236.2715883-2-yosryahmed@google.com > in mm-hotfixes-unstable. Don't know what to do with it. Please drop this one. > > I have no patch "mm: zswap: use SRCU to synchronize with CPU hotunplug" > in mm-unstable. , and keep that one dropped. I will send another patch this week on top of mm-hotfixes-unstable, but that should be separate. The revert should land in v6.13 regardless. Thanks! > > > > From: Yosry Ahmed > Subject: Revert "mm: zswap: fix race between [de]compression and CPU hotu= nplug" > Date: Tue, 7 Jan 2025 22:22:34 +0000 > > 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= : > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D > 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 m= m/zswap.c:886 [inline] > ffffffff8e7d2ed0 (cpu_hotplug_lock){++++}-{0:0}, at: zswap_compress mm/z= swap.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+0xa74/0= x1ba0 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/vm= scan.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/vms= can.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-0000= 6-g5428dc1906dd #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS G= oogle 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. > > Link: https://lkml.kernel.org/r/20250107222236.2715883-1-yosryahmed@googl= e.com > Signed-off-by: Yosry Ahmed > Reported-by: syzbot > Cc: Barry Song > Cc: Chengming Zhou > Cc: Johannes Weiner > Cc: Kanchana P Sridhar > Cc: Nhat Pham > Cc: Sam Sun > Cc: Vitaly Wool > Cc: > Signed-off-by: Andrew Morton > --- > > mm/zswap.c | 19 +++---------------- > 1 file changed, 3 insertions(+), 16 deletions(-) > > --- a/mm/zswap.c~revert-mm-zswap-fix-race-between-compression-and-cpu-hot= unplug > +++ a/mm/zswap.c > @@ -880,18 +880,6 @@ static int zswap_cpu_comp_dead(unsigned > 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_ct= x __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 * > gfp_t gfp; > u8 *dst; > > - acomp_ctx =3D acomp_ctx_get_cpu(pool->acomp_ctx); > + acomp_ctx =3D raw_cpu_ptr(pool->acomp_ctx); > + > mutex_lock(&acomp_ctx->mutex); > > dst =3D acomp_ctx->buffer; > @@ -961,7 +950,6 @@ unlock: > zswap_reject_alloc_fail++; > > mutex_unlock(&acomp_ctx->mutex); > - acomp_ctx_put_cpu(); > return comp_ret =3D=3D 0 && alloc_ret =3D=3D 0; > } > > @@ -972,7 +960,7 @@ static void zswap_decompress(struct zswa > struct crypto_acomp_ctx *acomp_ctx; > u8 *src; > > - acomp_ctx =3D acomp_ctx_get_cpu(entry->pool->acomp_ctx); > + acomp_ctx =3D raw_cpu_ptr(entry->pool->acomp_ctx); > mutex_lock(&acomp_ctx->mutex); > > src =3D zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO); > @@ -1002,7 +990,6 @@ static void zswap_decompress(struct zswa > > if (src !=3D acomp_ctx->buffer) > zpool_unmap_handle(zpool, entry->handle); > - acomp_ctx_put_cpu(); > } > > /********************************* > _ >