Re: [moderation/CI] Re: mm/mglru: fix lockless folio_putback_lru() race in evict_folios()

#syz upstream

On Fri, Aug 7, 2026 at 6:41 PM syzbot ci
<[email protected]> wrote:
>
> syzbot ci has tested the following series
>
> [v1] mm/mglru: fix lockless folio_putback_lru() race in evict_folios()
> https://lore.kernel.org/all/[email protected]
> * [PATCH] mm/mglru: fix lockless folio_putback_lru() race in evict_folios()
>
> and found the following issue:
> possible deadlock in __folio_batch_add_and_move
>
> Full report is available here:
> https://ci.syzbot.org/series/84ef3e36-11bb-4ace-93cf-a1d457206afc
>
> ***
>
> possible deadlock in __folio_batch_add_and_move
>
> tree:      linux-next
> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next
> base:      ea2bff00da89d7767d677bb68470130ba96f4928
> arch:      amd64
> compiler:  Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
> config:    https://ci.syzbot.org/builds/fefee38b-873a-46f2-b7ad-f80279b083f8/config
> syz repro: https://ci.syzbot.org/findings/9a05a8ec-c7b9-47ec-8888-0383f37b235c/syz_repro
>
> ======================================================
> WARNING: possible circular locking dependency detected
> syzkaller #0 Not tainted
> ------------------------------------------------------
> syz.0.17/5796 is trying to acquire lock:
> ffff888121033c10 (lock#3){+.+.}-{3:3}, at: local_lock_acquire include/linux/local_lock_internal.h:46 [inline]
> ffff888121033c10 (lock#3){+.+.}-{3:3}, at: __folio_batch_add_and_move+0x11a/0xc50 mm/folio.c:220
>
> but task is already holding lock:
> ffff888102ab6cb0 (&lruvec->lru_lock){....}-{3:3}, at: spin_lock_irq include/linux/spinlock.h:372 [inline]
> ffff888102ab6cb0 (&lruvec->lru_lock){....}-{3:3}, at: evict_folios+0x3cf5/0x4970 mm/vmscan.c:4926
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&lruvec->lru_lock){....}-{3:3}:
>        __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
>        _raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:166
>        folio_lruvec_lock_irqsave+0x273/0x550 mm/memcontrol.c:1509
>        folio_lruvec_relock_irqsave include/linux/memcontrol.h:1567 [inline]
>        folio_batch_move_lru+0x6d3/0xa60 mm/folio.c:192
>        __folio_batch_add_and_move+0x510/0xc50 mm/folio.c:224
>        shmem_alloc_and_add_folio+0xcc2/0xf60 mm/shmem.c:2033
>        shmem_get_folio_gfp+0x5da/0x16d0 mm/shmem.c:2527
>        shmem_read_folio_gfp+0x8a/0xe0 mm/shmem.c:5964
>        drm_gem_get_pages+0x253/0x9c0 drivers/gpu/drm/drm_gem.c:695
>        drm_gem_shmem_get_pages_locked+0x22b/0x480 drivers/gpu/drm/drm_gem_shmem_helper.c:242
>        drm_gem_shmem_pin_locked+0x251/0x510 drivers/gpu/drm/drm_gem_shmem_helper.c:305
>        drm_gem_shmem_vmap_locked+0x487/0x7d0 drivers/gpu/drm/drm_gem_shmem_helper.c:409
>        drm_gem_vmap_locked drivers/gpu/drm/drm_gem.c:1421 [inline]
>        drm_gem_vmap+0x10a/0x1d0 drivers/gpu/drm/drm_gem.c:1463
>        drm_client_buffer_vmap+0x6c/0xb0 drivers/gpu/drm/drm_client.c:356
>        drm_fbdev_shmem_driver_fbdev_probe+0x280/0x930 drivers/gpu/drm/drm_fbdev_shmem.c:159
>        drm_fb_helper_single_fb_probe drivers/gpu/drm/drm_fb_helper.c:1544 [inline]
>        __drm_fb_helper_initial_config_and_unlock+0x148f/0x1b50 drivers/gpu/drm/drm_fb_helper.c:1725
>        drm_fbdev_client_hotplug+0x16c/0x230 drivers/gpu/drm/clients/drm_fbdev_client.c:66
>        drm_client_register+0x16e/0x200 drivers/gpu/drm/drm_client.c:143
>        drm_fbdev_client_setup+0x1a0/0x450 drivers/gpu/drm/clients/drm_fbdev_client.c:168
>        drm_client_setup+0x107/0x220 drivers/gpu/drm/clients/drm_client_setup.c:46
>        bochs_pci_probe+0xa9a/0xbb0 drivers/gpu/drm/tiny/bochs.c:776
>        local_pci_probe drivers/pci/pci-driver.c:354 [inline]
>        pci_call_probe drivers/pci/pci-driver.c:416 [inline]
>        __pci_device_probe drivers/pci/pci-driver.c:478 [inline]
>        pci_device_probe+0x48e/0xd10 drivers/pci/pci-driver.c:512
>        call_driver_probe drivers/base/dd.c:-1 [inline]
>        really_probe+0x254/0xae0 drivers/base/dd.c:706
>        __driver_probe_device+0x1e8/0x360 drivers/base/dd.c:868
>        driver_probe_device+0x4f/0x240 drivers/base/dd.c:898
>        __driver_attach+0x339/0x600 drivers/base/dd.c:1292
>        bus_for_each_dev+0x23b/0x2c0 drivers/base/bus.c:383
>        bus_add_driver+0x345/0x670 drivers/base/bus.c:763
>        driver_register+0x23a/0x320 drivers/base/driver.c:174
>        do_one_initcall+0x250/0x870 init/main.c:1359
>        do_initcall_level+0x10a/0x1a0 init/main.c:1421
>        do_initcalls+0x59/0xa0 init/main.c:1437
>        kernel_init_freeable+0x29d/0x3e0 init/main.c:1672
>        kernel_init+0x22/0x1d0 init/main.c:1562
>        ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>
> -> #0 (lock#3){+.+.}-{3:3}:
>        check_prev_add kernel/locking/lockdep.c:3181 [inline]
>        check_prevs_add kernel/locking/lockdep.c:3300 [inline]
>        validate_chain kernel/locking/lockdep.c:3924 [inline]
>        __lock_acquire+0x15ff/0x2e50 kernel/locking/lockdep.c:5254
>        lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908
>        local_lock_acquire include/linux/local_lock_internal.h:46 [inline]
>        __folio_batch_add_and_move+0x132/0xc50 mm/folio.c:220
>        folio_putback_lru+0x18/0xe0 mm/vmscan.c:822
>        evict_folios+0x3cfd/0x4970 mm/vmscan.c:4927
>        try_to_shrink_lruvec+0xe3b/0x1340 mm/vmscan.c:5081
>        lru_gen_shrink_lruvec mm/vmscan.c:5226 [inline]
>        shrink_lruvec+0x54f/0x2c40 mm/vmscan.c:5986
>        shrink_node_memcgs mm/vmscan.c:6225 [inline]
>        shrink_node+0xa9b/0x3e30 mm/vmscan.c:6269
>        shrink_zones mm/vmscan.c:6508 [inline]
>        do_try_to_free_pages+0x6a3/0x1990 mm/vmscan.c:6570
>        try_to_free_mem_cgroup_pages+0x30d/0x830 mm/vmscan.c:6892
>        mem_cgroup_resize_max+0x23c/0x470 mm/memcontrol-v1.c:1817
>        mem_cgroup_write+0x223/0x290 mm/memcontrol-v1.c:-1
>        cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4412
>        kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
>        new_sync_write fs/read_write.c:595 [inline]
>        vfs_write+0x612/0xba0 fs/read_write.c:687
>        ksys_write+0x150/0x270 fs/read_write.c:739
>        do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
>        do_syscall_64+0x166/0x510 arch/x86/entry/syscall_64.c:84
>        entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> other info that might help us debug this:
>
>  Possible unsafe locking scenario:
>
>        CPU0                    CPU1
>        ----                    ----
>   lock(&lruvec->lru_lock);
>                                lock(lock#3);
>                                lock(&lruvec->lru_lock);
>   lock(lock#3);
>
>  *** DEADLOCK ***
>
> locks held by syz.0.17/5796: 5, last CPU#0:
>  #0: ffff88810338ecf0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320 fs/file.c:1259
>  #1: ffff888110422460 (sb_writers#10){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2754 [inline]
>  #1: ffff888110422460 (sb_writers#10){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0 fs/read_write.c:683
>  #2: ffff88811ad85880 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d8/0x540 fs/kernfs/file.c:336
>  #3: ffff8881bd86d3c8 (kn->active#53){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:73 [inline]
>  #3: ffff8881bd86d3c8 (kn->active#53){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x22b/0x540 fs/kernfs/file.c:337
>  #4: ffff888102ab6cb0 (&lruvec->lru_lock){....}-{3:3}, at: spin_lock_irq include/linux/spinlock.h:372 [inline]
>  #4: ffff888102ab6cb0 (&lruvec->lru_lock){....}-{3:3}, at: evict_folios+0x3cf5/0x4970 mm/vmscan.c:4926
>
> stack backtrace:
> CPU: 0 UID: 0 PID: 5796 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
>  print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2059
>  check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2191
>  check_prev_add kernel/locking/lockdep.c:3181 [inline]
>  check_prevs_add kernel/locking/lockdep.c:3300 [inline]
>  validate_chain kernel/locking/lockdep.c:3924 [inline]
>  __lock_acquire+0x15ff/0x2e50 kernel/locking/lockdep.c:5254
>  lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908
>  local_lock_acquire include/linux/local_lock_internal.h:46 [inline]
>  __folio_batch_add_and_move+0x132/0xc50 mm/folio.c:220
>  folio_putback_lru+0x18/0xe0 mm/vmscan.c:822
>  evict_folios+0x3cfd/0x4970 mm/vmscan.c:4927
>  try_to_shrink_lruvec+0xe3b/0x1340 mm/vmscan.c:5081
>  lru_gen_shrink_lruvec mm/vmscan.c:5226 [inline]
>  shrink_lruvec+0x54f/0x2c40 mm/vmscan.c:5986
>  shrink_node_memcgs mm/vmscan.c:6225 [inline]
>  shrink_node+0xa9b/0x3e30 mm/vmscan.c:6269
>  shrink_zones mm/vmscan.c:6508 [inline]
>  do_try_to_free_pages+0x6a3/0x1990 mm/vmscan.c:6570
>  try_to_free_mem_cgroup_pages+0x30d/0x830 mm/vmscan.c:6892
>  mem_cgroup_resize_max+0x23c/0x470 mm/memcontrol-v1.c:1817
>  mem_cgroup_write+0x223/0x290 mm/memcontrol-v1.c:-1
>  cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4412
>  kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
>  new_sync_write fs/read_write.c:595 [inline]
>  vfs_write+0x612/0xba0 fs/read_write.c:687
>  ksys_write+0x150/0x270 fs/read_write.c:739
>  do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
>  do_syscall_64+0x166/0x510 arch/x86/entry/syscall_64.c:84
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f64a439e0d9
> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f64a5333028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 00007f64a4625fa0 RCX: 00007f64a439e0d9
> RDX: 0000000000000020 RSI: 00002000000002c0 RDI: 0000000000000003
> RBP: 00007f64a4435024 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f64a4626038 R14: 00007f64a4625fa0 R15: 00007fff0f9eaaa8
>  </TASK>
>
>
> ***
>
> If these findings have caused you to resend the series or submit a
> separate fix, please add the following tag to your commit message:
>   Tested-by: [email protected]
>
> ---
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