Hello, I found a potential bug titled " possible deadlock in blk_mq_freeze_queue" with modified syzkaller in the Linux6.12.25(longterm maintenance, last updated on April 25, 2025) If you fix this issue, please add the following tag to the commit: Reported-by: Jianzhou Zhao luckd0g@163.com, xingwei lee xrivendell7@gmail.com The commit of the kernel is : ef4999852d307d38cfdecd91ed6892cc03beb9b8 kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=55f8591b98dd132 compiler: gcc version 11.4.0

Unfortunately, although my fuzz testing tool can trigger this bug relatively frequently, it still cannot generate a reproduction program.

------------[ cut here ]----------------------------------------- TITLE: possible deadlock in blk_mq_freeze_queue ------------[ cut here ]------------ loop6: detected capacity change from 1024 to 1023 ====================================================== WARNING: possible circular locking dependency detected 6.12.25 #1 Not tainted ------------------------------------------------------ syz.8.1968/32422 is trying to acquire lock: ffffffff8e34acc0 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:318 [inline] ffffffff8e34acc0 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4068 [inline] ffffffff8e34acc0 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4146 [inline] ffffffff8e34acc0 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_cache_noprof+0x56/0x3e0 mm/slub.c:4322

but task is already holding lock: ffff8880435f1468 (&q->q_usage_counter(io)#23){++++}-{0:0}, at: blk_freeze_queue block/blk-mq.c:224 [inline] ffff8880435f1468 (&q->q_usage_counter(io)#23){++++}-{0:0}, at: blk_mq_freeze_queue+0x15/0x20 block/blk-mq.c:234

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&q->q_usage_counter(io)#23){++++}-{0:0}: bio_queue_enter block/blk.h:76 [inline] blk_mq_submit_bio+0x22fd/0x2dd0 block/blk-mq.c:3088 __submit_bio+0x63b/0x10b0 block/blk-core.c:629 __submit_bio_noacct_mq block/blk-core.c:716 [inline] submit_bio_noacct_nocheck block/blk-core.c:745 [inline] submit_bio_noacct_nocheck+0x6cc/0xd30 block/blk-core.c:722 submit_bio_noacct+0x6c9/0x1fc0 block/blk-core.c:868 xfs_buf_ioapply_map fs/xfs/xfs_buf.c:1585 [inline] _xfs_buf_ioapply+0xa65/0xed0 fs/xfs/xfs_buf.c:1673 __xfs_buf_submit+0x26c/0x700 fs/xfs/xfs_buf.c:1757 xfs_buf_submit fs/xfs/xfs_buf.c:61 [inline] _xfs_buf_read fs/xfs/xfs_buf.c:808 [inline] xfs_buf_read_map+0x672/0xde0 fs/xfs/xfs_buf.c:872 xfs_trans_read_buf_map+0x356/0xcf0 fs/xfs/xfs_trans_buf.c:289 xfs_trans_read_buf fs/xfs/xfs_trans.h:212 [inline] xfs_imap_to_bp+0x110/0x2a0 fs/xfs/libxfs/xfs_inode_buf.c:138 xfs_inode_item_precommit+0x5d9/0x980 fs/xfs/xfs_inode_item.c:174 xfs_trans_run_precommits fs/xfs/xfs_trans.c:802 [inline] __xfs_trans_commit+0x303/0xda0 fs/xfs/xfs_trans.c:845 xfs_trans_commit+0x117/0x1b0 fs/xfs/xfs_trans.c:930 xfs_qm_qino_alloc+0x4da/0x700 fs/xfs/xfs_qm.c:861 xfs_qm_init_quotainos+0x526/0x6e0 fs/xfs/xfs_qm.c:1664 xfs_qm_init_quotainfo+0xf8/0xb00 fs/xfs/xfs_qm.c:667 xfs_qm_mount_quotas+0x59/0x650 fs/xfs/xfs_qm.c:1514 xfs_mountfs+0x1c0e/0x20e0 fs/xfs/xfs_mount.c:984 xfs_fs_fill_super+0x148f/0x1f30 fs/xfs/xfs_super.c:1764 get_tree_bdev_flags+0x389/0x620 fs/super.c:1636 vfs_get_tree+0x90/0x340 fs/super.c:1814 do_new_mount fs/namespace.c:3512 [inline] path_mount+0x1290/0x1bc0 fs/namespace.c:3839 do_mount+0xf8/0x110 fs/namespace.c:3852 __do_sys_mount fs/namespace.c:4062 [inline] __se_sys_mount fs/namespace.c:4039 [inline] __x64_sys_mount+0x193/0x230 fs/namespace.c:4039 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcf/0x250 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&xfs_nondir_ilock_class#3){++++}-{3:3}: down_write_nested+0x96/0x210 kernel/locking/rwsem.c:1693 xfs_ilock+0x35c/0x420 fs/xfs/xfs_inode.c:164 xfs_reclaim_inode fs/xfs/xfs_icache.c:981 [inline] xfs_icwalk_process_inode fs/xfs/xfs_icache.c:1675 [inline] xfs_icwalk_ag+0xa64/0x17c0 fs/xfs/xfs_icache.c:1757 xfs_icwalk+0x4b/0xa0 fs/xfs/xfs_icache.c:1805 xfs_reclaim_inodes_nr+0x1ad/0x2b0 fs/xfs/xfs_icache.c:1047 super_cache_scan+0x364/0x490 fs/super.c:227 do_shrink_slab+0x464/0x11d0 mm/shrinker.c:437 shrink_slab+0x336/0x12c0 mm/shrinker.c:664 shrink_one+0x4a8/0x7d0 mm/vmscan.c:4835 shrink_many mm/vmscan.c:4896 [inline] lru_gen_shrink_node mm/vmscan.c:4974 [inline] shrink_node+0x24da/0x3b50 mm/vmscan.c:5954 kswapd_shrink_node mm/vmscan.c:6782 [inline] balance_pgdat+0x9d0/0x1670 mm/vmscan.c:6974 kswapd+0x538/0xc70 mm/vmscan.c:7243 kthread+0x342/0x450 kernel/kthread.c:389 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:152 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

-> #0 (fs_reclaim){+.+.}-{0:0}: check_prev_add kernel/locking/lockdep.c:3161 [inline] check_prevs_add kernel/locking/lockdep.c:3280 [inline] validate_chain kernel/locking/lockdep.c:3904 [inline] __lock_acquire+0x2940/0x4810 kernel/locking/lockdep.c:5202 lock_acquire kernel/locking/lockdep.c:5825 [inline] lock_acquire+0x1b4/0x590 kernel/locking/lockdep.c:5790 __fs_reclaim_acquire mm/page_alloc.c:3853 [inline] fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:3867 might_alloc include/linux/sched/mm.h:318 [inline] slab_pre_alloc_hook mm/slub.c:4068 [inline] slab_alloc_node mm/slub.c:4146 [inline] __kmalloc_cache_noprof+0x56/0x3e0 mm/slub.c:4322 kmalloc_noprof include/linux/slab.h:878 [inline] kzalloc_noprof include/linux/slab.h:1014 [inline] kobject_uevent_env+0x23a/0x16b0 lib/kobject_uevent.c:540 set_capacity_and_notify+0x1cb/0x250 block/genhd.c:95 loop_set_size.isra.0+0x2f/0xc0 drivers/block/loop.c:232 loop_set_status+0x486/0x740 drivers/block/loop.c:1210 loop_set_status_old+0x148/0x1c0 drivers/block/loop.c:1313 lo_ioctl+0xc5e/0x1830 drivers/block/loop.c:1466 blkdev_ioctl+0x27b/0x6d0 block/ioctl.c:693 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl fs/ioctl.c:893 [inline] __x64_sys_ioctl+0x19d/0x210 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcf/0x250 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of: fs_reclaim --> &xfs_nondir_ilock_class#3 --> &q->q_usage_counter(io)#23

Possible unsafe locking scenario:

CPU0 CPU1 ---- ---- lock(&q->q_usage_counter(io)#23); lock(&xfs_nondir_ilock_class#3); lock(&q->q_usage_counter(io)#23); lock(fs_reclaim);

*** DEADLOCK ***

3 locks held by syz.8.1968/32422: #0: ffff888020454b70 (&lo->lo_mutex){+.+.}-{3:3}, at: loop_set_status+0x2a/0x740 drivers/block/loop.c:1176 #1: ffff8880435f1468 (&q->q_usage_counter(io)#23){++++}-{0:0}, at: blk_freeze_queue block/blk-mq.c:224 [inline] #1: ffff8880435f1468 (&q->q_usage_counter(io)#23){++++}-{0:0}, at: blk_mq_freeze_queue+0x15/0x20 block/blk-mq.c:234 #2: ffff8880435f14a0 (&q->q_usage_counter(queue)#7){+.+.}-{0:0}, at: blk_freeze_queue block/blk-mq.c:224 [inline] #2: ffff8880435f14a0 (&q->q_usage_counter(queue)#7){+.+.}-{0:0}, at: blk_mq_freeze_queue+0x15/0x20 block/blk-mq.c:234

stack backtrace: CPU: 0 UID: 0 PID: 32422 Comm: syz.8.1968 Not tainted 6.12.25 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1b0 lib/dump_stack.c:120 print_circular_bug.isra.0+0x5e5/0x9f0 kernel/locking/lockdep.c:2074 check_noncircular+0x2f1/0x3d0 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 kernel/locking/lockdep.c:3904 [inline] __lock_acquire+0x2940/0x4810 kernel/locking/lockdep.c:5202 lock_acquire kernel/locking/lockdep.c:5825 [inline] lock_acquire+0x1b4/0x590 kernel/locking/lockdep.c:5790 __fs_reclaim_acquire mm/page_alloc.c:3853 [inline] fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:3867 might_alloc include/linux/sched/mm.h:318 [inline] slab_pre_alloc_hook mm/slub.c:4068 [inline] slab_alloc_node mm/slub.c:4146 [inline] __kmalloc_cache_noprof+0x56/0x3e0 mm/slub.c:4322 kmalloc_noprof include/linux/slab.h:878 [inline] kzalloc_noprof include/linux/slab.h:1014 [inline] kobject_uevent_env+0x23a/0x16b0 lib/kobject_uevent.c:540 set_capacity_and_notify+0x1cb/0x250 block/genhd.c:95 loop_set_size.isra.0+0x2f/0xc0 drivers/block/loop.c:232 loop_set_status+0x486/0x740 drivers/block/loop.c:1210 loop_set_status_old+0x148/0x1c0 drivers/block/loop.c:1313 lo_ioctl+0xc5e/0x1830 drivers/block/loop.c:1466 blkdev_ioctl+0x27b/0x6d0 block/ioctl.c:693 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl fs/ioctl.c:893 [inline] __x64_sys_ioctl+0x19d/0x210 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcf/0x250 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f22897ac5ad Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 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 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f228a5f2f98 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007f22899e5fa0 RCX: 00007f22897ac5ad RDX: 0000200000000080 RSI: 0000000000004c02 RDI: 0000000000000006 RBP: 00007f228984458e R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007f22899e5fa0 R15: 00007f228a5d3000 </TASK>

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I hope it helps. Best regards Jianzhou Zhao