syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
udevd/19558 is trying to acquire lock:
ffffffff8e449180 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:317 [inline]
ffffffff8e449180 (fs_reclaim){+.+.}-{0:0}, at: mempool_alloc_noprof+0xab/0x2f0 mm/mempool.c:559

but task is already holding lock:
ffff888141be6498 (set->srcu){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:185 [inline]
ffff888141be6498 (set->srcu){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:277 [inline]
ffff888141be6498 (set->srcu){.+.+}-{0:0}, at: blk_mq_dispatch_queue_requests+0x5f9/0x800 block/blk-mq.c:2897

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (set->srcu){.+.+}-{0:0}:
       srcu_lock_sync include/linux/srcu.h:197 [inline]
       __synchronize_srcu+0x96/0x390 kernel/rcu/srcutree.c:1503
       blk_throtl_init+0x298/0x410 block/blk-throttle.c:1324
       tg_set_conf+0x1c6/0x4b0 block/blk-throttle.c:1359
       cgroup_file_write+0x3a1/0x740 kernel/cgroup/cgroup.c:4312
       kernfs_fop_write_iter+0x3af/0x540 fs/kernfs/file.c:352
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x5c9/0xb30 fs/read_write.c:686
       ksys_write+0x145/0x250 fs/read_write.c:738
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&q->q_usage_counter(io)#17){++++}-{0:0}:
       blk_alloc_queue+0x538/0x620 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4410 [inline]
       __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4457
       loop_add+0x411/0xad0 drivers/block/loop.c:2206
       loop_init+0xd9/0x170 drivers/block/loop.c:2441
       do_one_initcall+0x1fb/0x820 init/main.c:1378
       do_initcall_level+0x104/0x190 init/main.c:1440
       do_initcalls+0x59/0xa0 init/main.c:1456
       kernel_init_freeable+0x334/0x4b0 init/main.c:1688
       kernel_init+0x1d/0x1d0 init/main.c:1578
       ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

-> #0 (fs_reclaim){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
       __fs_reclaim_acquire mm/page_alloc.c:4301 [inline]
       fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4315
       might_alloc include/linux/sched/mm.h:317 [inline]
       mempool_alloc_noprof+0xab/0x2f0 mm/mempool.c:559
       bio_alloc_bioset+0x241/0x12a0 block/bio.c:559
       __blkdev_direct_IO_async block/fops.c:338 [inline]
       blkdev_direct_IO+0x9c0/0x17e0 block/fops.c:437
       blkdev_read_iter+0x23d/0x440 block/fops.c:845
       lo_submit_rw_aio+0x488/0x620 drivers/block/loop.c:-1
       lo_rw_aio_nowait drivers/block/loop.c:513 [inline]
       loop_queue_rq+0x6c5/0x8d0 drivers/block/loop.c:2036
       __blk_mq_issue_directly block/blk-mq.c:2714 [inline]
       blk_mq_request_issue_directly+0x3c1/0x710 block/blk-mq.c:2801
       blk_mq_issue_direct+0x2a0/0x660 block/blk-mq.c:2822
       blk_mq_dispatch_queue_requests+0x621/0x800 block/blk-mq.c:2897
       blk_mq_flush_plug_list+0x432/0x550 block/blk-mq.c:2980
       __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1225
       blk_finish_plug block/blk-core.c:1252 [inline]
       __submit_bio+0x2d3/0x5a0 block/blk-core.c:651
       __submit_bio_noacct_mq block/blk-core.c:724 [inline]
       submit_bio_noacct_nocheck+0x2eb/0xa30 block/blk-core.c:755
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x7b7/0x830 fs/buffer.c:2461
       filemap_read_folio+0x117/0x380 mm/filemap.c:2496
       do_read_cache_folio+0x358/0x590 mm/filemap.c:4096
       read_mapping_folio include/linux/pagemap.h:1017 [inline]
       read_part_sector+0xb6/0x2b0 block/partitions/core.c:722
       adfspart_check_ICS+0xa4/0xa50 block/partitions/acorn.c:360
       check_partition block/partitions/core.c:141 [inline]
       blk_add_partitions block/partitions/core.c:589 [inline]
       bdev_disk_changed+0x75f/0x14b0 block/partitions/core.c:693
       blkdev_get_whole+0x380/0x510 block/bdev.c:765
       bdev_open+0x31e/0xd30 block/bdev.c:974
       blkdev_open+0x457/0x600 block/fops.c:703
       do_dentry_open+0x7ce/0x1420 fs/open.c:962
       vfs_open+0x3b/0x340 fs/open.c:1094
       do_open fs/namei.c:4597 [inline]
       path_openat+0x33ce/0x3d90 fs/namei.c:4756
       do_filp_open+0x1fa/0x410 fs/namei.c:4783
       do_sys_openat2+0x121/0x200 fs/open.c:1430
       do_sys_open fs/open.c:1436 [inline]
       __do_sys_openat fs/open.c:1452 [inline]
       __se_sys_openat fs/open.c:1447 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1447
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  fs_reclaim --> &q->q_usage_counter(io)#17 --> set->srcu

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(set->srcu);
                               lock(&q->q_usage_counter(io)#17);
                               lock(set->srcu);
  lock(fs_reclaim);

 *** DEADLOCK ***

2 locks held by udevd/19558:
 #0: ffff8880253b7358 (&disk->open_mutex){+.+.}-{4:4}, at: bdev_open+0xe0/0xd30 block/bdev.c:962
 #1: ffff888141be6498 (set->srcu){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:185 [inline]
 #1: ffff888141be6498 (set->srcu){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:277 [inline]
 #1: ffff888141be6498 (set->srcu){.+.+}-{0:0}, at: blk_mq_dispatch_queue_requests+0x5f9/0x800 block/blk-mq.c:2897

stack backtrace:
CPU: 1 UID: 0 PID: 19558 Comm: udevd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
 __fs_reclaim_acquire mm/page_alloc.c:4301 [inline]
 fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4315
 might_alloc include/linux/sched/mm.h:317 [inline]
 mempool_alloc_noprof+0xab/0x2f0 mm/mempool.c:559
 bio_alloc_bioset+0x241/0x12a0 block/bio.c:559
 __blkdev_direct_IO_async block/fops.c:338 [inline]
 blkdev_direct_IO+0x9c0/0x17e0 block/fops.c:437
 blkdev_read_iter+0x23d/0x440 block/fops.c:845
 lo_submit_rw_aio+0x488/0x620 drivers/block/loop.c:-1
 lo_rw_aio_nowait drivers/block/loop.c:513 [inline]
 loop_queue_rq+0x6c5/0x8d0 drivers/block/loop.c:2036
 __blk_mq_issue_directly block/blk-mq.c:2714 [inline]
 blk_mq_request_issue_directly+0x3c1/0x710 block/blk-mq.c:2801
 blk_mq_issue_direct+0x2a0/0x660 block/blk-mq.c:2822
 blk_mq_dispatch_queue_requests+0x621/0x800 block/blk-mq.c:2897
 blk_mq_flush_plug_list+0x432/0x550 block/blk-mq.c:2980
 __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1225
 blk_finish_plug block/blk-core.c:1252 [inline]
 __submit_bio+0x2d3/0x5a0 block/blk-core.c:651
 __submit_bio_noacct_mq block/blk-core.c:724 [inline]
 submit_bio_noacct_nocheck+0x2eb/0xa30 block/blk-core.c:755
 submit_bh fs/buffer.c:2829 [inline]
 block_read_full_folio+0x7b7/0x830 fs/buffer.c:2461
 filemap_read_folio+0x117/0x380 mm/filemap.c:2496
 do_read_cache_folio+0x358/0x590 mm/filemap.c:4096
 read_mapping_folio include/linux/pagemap.h:1017 [inline]
 read_part_sector+0xb6/0x2b0 block/partitions/core.c:722
 adfspart_check_ICS+0xa4/0xa50 block/partitions/acorn.c:360
 check_partition block/partitions/core.c:141 [inline]
 blk_add_partitions block/partitions/core.c:589 [inline]
 bdev_disk_changed+0x75f/0x14b0 block/partitions/core.c:693
 blkdev_get_whole+0x380/0x510 block/bdev.c:765
 bdev_open+0x31e/0xd30 block/bdev.c:974
 blkdev_open+0x457/0x600 block/fops.c:703
 do_dentry_open+0x7ce/0x1420 fs/open.c:962
 vfs_open+0x3b/0x340 fs/open.c:1094
 do_open fs/namei.c:4597 [inline]
 path_openat+0x33ce/0x3d90 fs/namei.c:4756
 do_filp_open+0x1fa/0x410 fs/namei.c:4783
 do_sys_openat2+0x121/0x200 fs/open.c:1430
 do_sys_open fs/open.c:1436 [inline]
 __do_sys_openat fs/open.c:1452 [inline]
 __se_sys_openat fs/open.c:1447 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1447
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5ecd2a7407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffcb6778a00 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f5ecda5d880 RCX: 00007f5ecd2a7407
RDX: 00000000000a0800 RSI: 00005567f043f280 RDI: ffffffffffffff9c
RBP: 00005567f0430910 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00005567f0448e00
R13: 00005567f043e190 R14: 0000000000000000 R15: 00005567f0448e00
 </TASK>