[syzbot] [bcachefs?] possible deadlock in __bch2_count_fsck_err

syzbot
2025-05-16T09:37:29Z

Hello,

syzbot found the following issue on:

HEAD commit: c32f8dc5aaf9 Merge branch 'for-next/core' into for-kernelci
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=17b6a2f4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ea4635ffd6ad5b4a
dashboard link: https://syzkaller.appspot.com/bug?extid=2648414dd66587a935e2
compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
userspace arch: arm64

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b921498959d4/disk-c32f8dc5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/04e6ad946c4b/vmlinux-c32f8dc5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d4f0d8db50ee/Image-c32f8dc5.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2648414dd66587a935e2@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.15.0-rc5-syzkaller-gc32f8dc5aaf9 #0 Not tainted
------------------------------------------------------
syz.1.109/7273 is trying to acquire lock:
ffff0000f7e61448 (&c->fsck_error_msgs_lock){+.+.}-{4:4}, at: __bch2_count_fsck_err+0x58/0x98 fs/bcachefs/error.c:385

but task is already holding lock:
ffff0000f1fb1558 (&inode->ei_quota_lock){+.+.}-{4:4}, at: bch2_i_sectors_acct fs/bcachefs/fs-io.h:137 [inline]
ffff0000f1fb1558 (&inode->ei_quota_lock){+.+.}-{4:4}, at: bchfs_fpunch+0x228/0x404 fs/bcachefs/fs-io.c:578

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #9 (&inode->ei_quota_lock){+.+.}-{4:4}:
__mutex_lock_common+0x1d0/0x2190 kernel/locking/mutex.c:601
__mutex_lock kernel/locking/mutex.c:746 [inline]
mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:798
bch2_quota_reservation_add fs/bcachefs/fs-io.h:97 [inline]
__bch2_folio_reservation_get+0x5c0/0xa00 fs/bcachefs/fs-io-pagecache.c:460
bch2_folio_reservation_get fs/bcachefs/fs-io-pagecache.c:477 [inline]
bch2_page_mkwrite+0xa48/0xd60 fs/bcachefs/fs-io-pagecache.c:637
do_page_mkwrite+0x138/0x2b8 mm/memory.c:3287
wp_page_shared mm/memory.c:3688 [inline]
do_wp_page+0x1b54/0x43a8 mm/memory.c:3907
handle_pte_fault mm/memory.c:6013 [inline]
__handle_mm_fault mm/memory.c:6140 [inline]
handle_mm_fault+0x1064/0x4cec mm/memory.c:6309
do_page_fault+0x428/0x1554 arch/arm64/mm/fault.c:647
do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:919
el0_da+0x64/0x160 arch/arm64/kernel/entry-common.c:627
el0t_64_sync_handler+0x84/0x108 arch/arm64/kernel/entry-common.c:789
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

-> #8 (sb_pagefaults#3){.+.+}-{0:0}:
percpu_down_read include/linux/percpu-rwsem.h:52 [inline]
__sb_start_write include/linux/fs.h:1783 [inline]
sb_start_pagefault include/linux/fs.h:1948 [inline]
bch2_page_mkwrite+0x260/0xd60 fs/bcachefs/fs-io-pagecache.c:614
do_page_mkwrite+0x138/0x2b8 mm/memory.c:3287
wp_page_shared mm/memory.c:3688 [inline]
do_wp_page+0x1b54/0x43a8 mm/memory.c:3907
handle_pte_fault mm/memory.c:6013 [inline]
__handle_mm_fault mm/memory.c:6140 [inline]
handle_mm_fault+0x1064/0x4cec mm/memory.c:6309
do_page_fault+0x428/0x1554 arch/arm64/mm/fault.c:647
do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:919
el0_da+0x64/0x160 arch/arm64/kernel/entry-common.c:627
el0t_64_sync_handler+0x84/0x108 arch/arm64/kernel/entry-common.c:789
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

-> #7 (vm_lock){++++}-{0:0}:
__vma_enter_locked+0x184/0x354 mm/memory.c:6473
__vma_start_write+0x34/0x158 mm/memory.c:6497
vma_start_write include/linux/mm.h:829 [inline]
vma_expand+0x1b8/0x8f0 mm/vma.c:1086
relocate_vma_down+0x234/0x400 mm/mmap.c:1767
setup_arg_pages+0x4b4/0x920 fs/exec.c:800
load_elf_binary+0x8c4/0x1ebc fs/binfmt_elf.c:1019
search_binary_handler fs/exec.c:1778 [inline]
exec_binprm fs/exec.c:1810 [inline]
bprm_execve+0x77c/0x10dc fs/exec.c:1862
kernel_execve+0x70c/0x7f4 fs/exec.c:2028
run_init_process+0x1bc/0x1ec init/main.c:1378
try_to_run_init_process+0x20/0x7c init/main.c:1385
kernel_init+0xa8/0x1dc init/main.c:1513
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847

-> #6 (&mm->mmap_lock){++++}-{4:4}:
__might_fault+0xc4/0x124 mm/memory.c:7151
drm_mode_setcrtc+0xdc0/0x182c drivers/gpu/drm/drm_crtc.c:840
drm_ioctl_kernel+0x238/0x310 drivers/gpu/drm/drm_ioctl.c:796
drm_ioctl+0x65c/0xa5c drivers/gpu/drm/drm_ioctl.c:893
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl fs/ioctl.c:892 [inline]
__arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:892
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
el0_svc+0x58/0x17c arch/arm64/kernel/entry-common.c:767
el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:786
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

-> #5 (crtc_ww_class_mutex){+.+.}-{4:4}:
ww_acquire_init include/linux/ww_mutex.h:162 [inline]
drm_modeset_acquire_init+0x1d8/0x374 drivers/gpu/drm/drm_modeset_lock.c:250
drmm_mode_config_init+0xb0c/0x10d8 drivers/gpu/drm/drm_mode_config.c:462
vkms_modeset_init drivers/gpu/drm/vkms/vkms_drv.c:146 [inline]
vkms_create drivers/gpu/drm/vkms/vkms_drv.c:207 [inline]
vkms_init+0x2c0/0x5ac drivers/gpu/drm/vkms/vkms_drv.c:242
do_one_initcall+0x250/0x990 init/main.c:1257
do_initcall_level+0x154/0x214 init/main.c:1319
do_initcalls+0x84/0xf4 init/main.c:1335
do_basic_setup+0x8c/0xa0 init/main.c:1354
kernel_init_freeable+0x2dc/0x444 init/main.c:1567
kernel_init+0x24/0x1dc init/main.c:1457
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847

-> #4 (crtc_ww_class_acquire){+.+.}-{0:0}:
ww_acquire_init include/linux/ww_mutex.h:161 [inline]
drm_modeset_acquire_init+0x1b8/0x374 drivers/gpu/drm/drm_modeset_lock.c:250
drm_client_modeset_commit_atomic+0xcc/0x6ac drivers/gpu/drm/drm_client_modeset.c:1018
drm_client_modeset_commit_locked+0xd0/0x4a0 drivers/gpu/drm/drm_client_modeset.c:1182
drm_client_modeset_commit+0x50/0x7c drivers/gpu/drm/drm_client_modeset.c:1208
__drm_fb_helper_restore_fbdev_mode_unlocked+0x94/0x198 drivers/gpu/drm/drm_fb_helper.c:237
drm_fb_helper_set_par+0xa4/0x108 drivers/gpu/drm/drm_fb_helper.c:1359
fbcon_init+0xe4c/0x1d18 drivers/video/fbdev/core/fbcon.c:1112
visual_init+0x27c/0x540 drivers/tty/vt/vt.c:1011
do_bind_con_driver+0x7b8/0xdd8 drivers/tty/vt/vt.c:3831
do_take_over_console+0x824/0x97c drivers/tty/vt/vt.c:4397
do_fbcon_takeover+0x158/0x25c drivers/video/fbdev/core/fbcon.c:548
do_fb_registered drivers/video/fbdev/core/fbcon.c:2989 [inline]
fbcon_fb_registered+0x354/0x4c8 drivers/video/fbdev/core/fbcon.c:3009
do_register_framebuffer drivers/video/fbdev/core/fbmem.c:449 [inline]
register_framebuffer+0x44c/0x5ec drivers/video/fbdev/core/fbmem.c:515
__drm_fb_helper_initial_config_and_unlock+0x103c/0x159c drivers/gpu/drm/drm_fb_helper.c:1851
drm_fb_helper_initial_config+0x3c/0x58 drivers/gpu/drm/drm_fb_helper.c:1916
drm_fbdev_client_hotplug+0x154/0x22c drivers/gpu/drm/clients/drm_fbdev_client.c:52
drm_client_register+0x13c/0x1d4 drivers/gpu/drm/drm_client.c:140
drm_fbdev_client_setup+0x194/0x3d0 drivers/gpu/drm/clients/drm_fbdev_client.c:159
drm_client_setup+0x78/0x140 drivers/gpu/drm/clients/drm_client_setup.c:39
vkms_create drivers/gpu/drm/vkms/vkms_drv.c:218 [inline]
vkms_init+0x4b8/0x5ac drivers/gpu/drm/vkms/vkms_drv.c:242
do_one_initcall+0x250/0x990 init/main.c:1257
do_initcall_level+0x154/0x214 init/main.c:1319
do_initcalls+0x84/0xf4 init/main.c:1335
do_basic_setup+0x8c/0xa0 init/main.c:1354
kernel_init_freeable+0x2dc/0x444 init/main.c:1567
kernel_init+0x24/0x1dc init/main.c:1457
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847

-> #3 (&client->modeset_mutex){+.+.}-{4:4}:
__mutex_lock_common+0x1d0/0x2190 kernel/locking/mutex.c:601
__mutex_lock kernel/locking/mutex.c:746 [inline]
mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:798
drm_client_modeset_probe+0x2f0/0x4e88 drivers/gpu/drm/drm_client_modeset.c:843
__drm_fb_helper_initial_config_and_unlock+0xf0/0x159c drivers/gpu/drm/drm_fb_helper.c:1828
drm_fb_helper_initial_config+0x3c/0x58 drivers/gpu/drm/drm_fb_helper.c:1916
drm_fbdev_client_hotplug+0x154/0x22c drivers/gpu/drm/clients/drm_fbdev_client.c:52
drm_client_register+0x13c/0x1d4 drivers/gpu/drm/drm_client.c:140
drm_fbdev_client_setup+0x194/0x3d0 drivers/gpu/drm/clients/drm_fbdev_client.c:159
drm_client_setup+0x78/0x140 drivers/gpu/drm/clients/drm_client_setup.c:39
vkms_create drivers/gpu/drm/vkms/vkms_drv.c:218 [inline]
vkms_init+0x4b8/0x5ac drivers/gpu/drm/vkms/vkms_drv.c:242
do_one_initcall+0x250/0x990 init/main.c:1257
do_initcall_level+0x154/0x214 init/main.c:1319
do_initcalls+0x84/0xf4 init/main.c:1335
do_basic_setup+0x8c/0xa0 init/main.c:1354
kernel_init_freeable+0x2dc/0x444 init/main.c:1567
kernel_init+0x24/0x1dc init/main.c:1457
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847

-> #2 (&helper->lock){+.+.}-{4:4}:
__mutex_lock_common+0x1d0/0x2190 kernel/locking/mutex.c:601
__mutex_lock kernel/locking/mutex.c:746 [inline]
mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:798
__drm_fb_helper_restore_fbdev_mode_unlocked+0x74/0x198 drivers/gpu/drm/drm_fb_helper.c:228
drm_fb_helper_set_par+0xa4/0x108 drivers/gpu/drm/drm_fb_helper.c:1359
fbcon_init+0xe4c/0x1d18 drivers/video/fbdev/core/fbcon.c:1112
visual_init+0x27c/0x540 drivers/tty/vt/vt.c:1011
do_bind_con_driver+0x7b8/0xdd8 drivers/tty/vt/vt.c:3831
do_take_over_console+0x824/0x97c drivers/tty/vt/vt.c:4397
do_fbcon_takeover+0x158/0x25c drivers/video/fbdev/core/fbcon.c:548
do_fb_registered drivers/video/fbdev/core/fbcon.c:2989 [inline]
fbcon_fb_registered+0x354/0x4c8 drivers/video/fbdev/core/fbcon.c:3009
do_register_framebuffer drivers/video/fbdev/core/fbmem.c:449 [inline]
register_framebuffer+0x44c/0x5ec drivers/video/fbdev/core/fbmem.c:515
__drm_fb_helper_initial_config_and_unlock+0x103c/0x159c drivers/gpu/drm/drm_fb_helper.c:1851
drm_fb_helper_initial_config+0x3c/0x58 drivers/gpu/drm/drm_fb_helper.c:1916
drm_fbdev_client_hotplug+0x154/0x22c drivers/gpu/drm/clients/drm_fbdev_client.c:52
drm_client_register+0x13c/0x1d4 drivers/gpu/drm/drm_client.c:140
drm_fbdev_client_setup+0x194/0x3d0 drivers/gpu/drm/clients/drm_fbdev_client.c:159
drm_client_setup+0x78/0x140 drivers/gpu/drm/clients/drm_client_setup.c:39
vkms_create drivers/gpu/drm/vkms/vkms_drv.c:218 [inline]
vkms_init+0x4b8/0x5ac drivers/gpu/drm/vkms/vkms_drv.c:242
do_one_initcall+0x250/0x990 init/main.c:1257
do_initcall_level+0x154/0x214 init/main.c:1319
do_initcalls+0x84/0xf4 init/main.c:1335
do_basic_setup+0x8c/0xa0 init/main.c:1354
kernel_init_freeable+0x2dc/0x444 init/main.c:1567
kernel_init+0x24/0x1dc init/main.c:1457
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847

-> #1 (console_lock){+.+.}-{0:0}:
console_lock+0x194/0x1ec kernel/printk/printk.c:2849
__bch2_print_string_as_lines fs/bcachefs/util.c:267 [inline]
bch2_print_string_as_lines+0x34/0x150 fs/bcachefs/util.c:286
__bch2_fsck_err+0xb5c/0xdd0 fs/bcachefs/error.c:562
__need_discard_or_freespace_err+0x14c/0x1cc fs/bcachefs/alloc_background.c:678
bch2_bucket_do_index+0x320/0x490 fs/bcachefs/alloc_background.c:729
bch2_trigger_alloc+0xd1c/0x2d54 fs/bcachefs/alloc_background.c:885
bch2_key_trigger fs/bcachefs/bkey_methods.h:88 [inline]
bch2_key_trigger_new fs/bcachefs/bkey_methods.h:116 [inline]
run_one_trans_trigger fs/bcachefs/btree_trans_commit.c:516 [inline]
bch2_trans_commit_run_triggers fs/bcachefs/btree_trans_commit.c:550 [inline]
__bch2_trans_commit+0x634/0x62d0 fs/bcachefs/btree_trans_commit.c:990
bch2_trans_commit fs/bcachefs/btree_update.h:195 [inline]
btree_update_nodes_written fs/bcachefs/btree_update_interior.c:705 [inline]
btree_interior_update_work+0xb80/0x1cfc fs/bcachefs/btree_update_interior.c:843
process_one_work+0x7e8/0x156c kernel/workqueue.c:3238
process_scheduled_works kernel/workqueue.c:3319 [inline]
worker_thread+0x958/0xed8 kernel/workqueue.c:3400
kthread+0x5fc/0x75c kernel/kthread.c:464
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847

-> #0 (&c->fsck_error_msgs_lock){+.+.}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3166 [inline]
check_prevs_add kernel/locking/lockdep.c:3285 [inline]
validate_chain kernel/locking/lockdep.c:3909 [inline]
__lock_acquire+0x1728/0x3058 kernel/locking/lockdep.c:5235
lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5866
__mutex_lock_common+0x1d0/0x2190 kernel/locking/mutex.c:601
__mutex_lock kernel/locking/mutex.c:746 [inline]
mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:798
__bch2_count_fsck_err+0x58/0x98 fs/bcachefs/error.c:385
__bch2_i_sectors_acct+0x328/0x3c4 fs/bcachefs/fs-io.c:155
bch2_i_sectors_acct fs/bcachefs/fs-io.h:138 [inline]
bchfs_fpunch+0x23c/0x404 fs/bcachefs/fs-io.c:578
bch2_fallocate_dispatch+0x378/0x4e0 fs/bcachefs/fs-io.c:838
vfs_fallocate+0x5cc/0x73c fs/open.c:338
ioctl_preallocate fs/ioctl.c:290 [inline]
file_ioctl fs/ioctl.c:-1 [inline]
do_vfs_ioctl+0x1d4c/0x2218 fs/ioctl.c:885
__do_sys_ioctl fs/ioctl.c:904 [inline]
__se_sys_ioctl fs/ioctl.c:892 [inline]
__arm64_sys_ioctl+0xe4/0x1c4 fs/ioctl.c:892
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
el0_svc+0x58/0x17c arch/arm64/kernel/entry-common.c:767
el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:786
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

other info that might help us debug this:

Chain exists of:
&c->fsck_error_msgs_lock --> sb_pagefaults#3 --> &inode->ei_quota_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&inode->ei_quota_lock);
lock(sb_pagefaults#3);
lock(&inode->ei_quota_lock);
lock(&c->fsck_error_msgs_lock);

*** DEADLOCK ***

3 locks held by syz.1.109/7273:
#0: ffff0000d8e5e420 (sb_writers#17){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:3041 [inline]
#0: ffff0000d8e5e420 (sb_writers#17){.+.+}-{0:0}, at: vfs_fallocate+0x564/0x73c fs/open.c:337
#1: ffff0000f1fb1078 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:867 [inline]
#1: ffff0000f1fb1078 (&sb->s_type->i_mutex_key#24){+.+.}-{4:4}, at: bch2_fallocate_dispatch+0x1a8/0x4e0 fs/bcachefs/fs-io.c:827
#2: ffff0000f1fb1558 (&inode->ei_quota_lock){+.+.}-{4:4}, at: bch2_i_sectors_acct fs/bcachefs/fs-io.h:137 [inline]
#2: ffff0000f1fb1558 (&inode->ei_quota_lock){+.+.}-{4:4}, at: bchfs_fpunch+0x228/0x404 fs/bcachefs/fs-io.c:578

stack backtrace:
CPU: 1 UID: 0 PID: 7273 Comm: syz.1.109 Not tainted 6.15.0-rc5-syzkaller-gc32f8dc5aaf9 #0 PREEMPT
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call trace:
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:466 (C)
__dump_stack+0x30/0x40 lib/dump_stack.c:94
dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
dump_stack+0x1c/0x28 lib/dump_stack.c:129
print_circular_bug+0x324/0x32c kernel/locking/lockdep.c:2079
check_noncircular+0x154/0x174 kernel/locking/lockdep.c:2211
check_prev_add kernel/locking/lockdep.c:3166 [inline]
check_prevs_add kernel/locking/lockdep.c:3285 [inline]
validate_chain kernel/locking/lockdep.c:3909 [inline]
__lock_acquire+0x1728/0x3058 kernel/locking/lockdep.c:5235
lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5866
__mutex_lock_common+0x1d0/0x2190 kernel/locking/mutex.c:601
__mutex_lock kernel/locking/mutex.c:746 [inline]
mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:798
__bch2_count_fsck_err+0x58/0x98 fs/bcachefs/error.c:385
__bch2_i_sectors_acct+0x328/0x3c4 fs/bcachefs/fs-io.c:155
bch2_i_sectors_acct fs/bcachefs/fs-io.h:138 [inline]
bchfs_fpunch+0x23c/0x404 fs/bcachefs/fs-io.c:578
bch2_fallocate_dispatch+0x378/0x4e0 fs/bcachefs/fs-io.c:838
vfs_fallocate+0x5cc/0x73c fs/open.c:338
ioctl_preallocate fs/ioctl.c:290 [inline]
file_ioctl fs/ioctl.c:-1 [inline]
do_vfs_ioctl+0x1d4c/0x2218 fs/ioctl.c:885
__do_sys_ioctl fs/ioctl.c:904 [inline]
__se_sys_ioctl fs/ioctl.c:892 [inline]
__arm64_sys_ioctl+0xe4/0x1c4 fs/ioctl.c:892
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
el0_svc+0x58/0x17c arch/arm64/kernel/entry-common.c:767
el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:786
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

---
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https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup