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36357fd23a
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:
<TASK>
__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
</TASK>
Revert the change. A different fix for the race with CPU hotunplug will
follow.
Link: https://lkml.kernel.org/r/20250107222236.2715883-1-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Sam Sun <samsun1006219@gmail.com>
Cc: Vitaly Wool <vitalywool@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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