Hello, syzbot found the following issue on: HEAD commit: ba5b053a Add linux-next specific files for 20210318 git tree: linux-next console output: https://syzkaller.appspot.com/x/log.txt?x=10cfb406d00000 kernel config: https://syzkaller.appspot.com/x/.config?x=cd6e556bdf0188e4 dashboard link: https://syzkaller.appspot.com/bug?extid=707d51092ab7b87b23df Unfortunately, I don't have any reproducer for this issue yet. IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+707d51092ab7b87b23df@xxxxxxxxxxxxxxxxxxxxxxxxx UDF-fs: warning (device loop4): udf_load_vrs: No VRS found UDF-fs: Scanning with blocksize 4096 failed ====================================================== WARNING: possible circular locking dependency detected 5.12.0-rc3-next-20210318-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor.4/13936 is trying to acquire lock: ffff88805cb9b138 ((wq_completion)loop292057088){+.+.}-{0:0}, at: flush_workqueue+0xe1/0x13e0 kernel/workqueue.c:2783 but task is already holding lock: ffff88801a730468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x95/0x14a0 drivers/block/loop.c:1278 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #6 (&lo->lo_mutex){+.+.}-{3:3}: __mutex_lock_common kernel/locking/mutex.c:952 [inline] __mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1099 lo_open drivers/block/loop.c:1983 [inline] lo_open+0xa1/0x130 drivers/block/loop.c:1965 __blkdev_get+0x135/0xa30 fs/block_dev.c:1302 blkdev_get_by_dev fs/block_dev.c:1454 [inline] blkdev_get_by_dev+0x26c/0x600 fs/block_dev.c:1422 blkdev_open+0x154/0x2b0 fs/block_dev.c:1551 do_dentry_open+0x4b9/0x11b0 fs/open.c:826 do_open fs/namei.c:3365 [inline] path_openat+0x1c0e/0x27e0 fs/namei.c:3498 do_filp_open+0x17e/0x3c0 fs/namei.c:3525 do_sys_openat2+0x16d/0x420 fs/open.c:1187 do_sys_open fs/open.c:1203 [inline] __do_sys_open fs/open.c:1211 [inline] __se_sys_open fs/open.c:1207 [inline] __x64_sys_open+0x119/0x1c0 fs/open.c:1207 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #5 (loop_ctl_mutex){+.+.}-{3:3}: __mutex_lock_common kernel/locking/mutex.c:952 [inline] __mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1099 loop_probe+0xc7/0x150 drivers/block/loop.c:2407 blk_request_module+0x111/0x1d0 block/genhd.c:769 blkdev_get_no_open+0x225/0x2b0 fs/block_dev.c:1368 blkdev_get_by_dev fs/block_dev.c:1440 [inline] blkdev_get_by_dev+0x1f9/0x600 fs/block_dev.c:1422 blkdev_open+0x154/0x2b0 fs/block_dev.c:1551 do_dentry_open+0x4b9/0x11b0 fs/open.c:826 do_open fs/namei.c:3365 [inline] path_openat+0x1c0e/0x27e0 fs/namei.c:3498 do_filp_open+0x17e/0x3c0 fs/namei.c:3525 do_sys_openat2+0x16d/0x420 fs/open.c:1187 do_sys_open fs/open.c:1203 [inline] __do_sys_openat fs/open.c:1219 [inline] __se_sys_openat fs/open.c:1214 [inline] __x64_sys_openat+0x13f/0x1f0 fs/open.c:1214 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #4 (major_names_lock){+.+.}-{3:3}: __mutex_lock_common kernel/locking/mutex.c:952 [inline] __mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1099 blkdev_show+0x27/0x160 block/genhd.c:263 devinfo_show+0xc1/0xf0 fs/proc/devices.c:22 seq_read_iter+0xb66/0x1220 fs/seq_file.c:269 proc_reg_read_iter+0x1fb/0x2d0 fs/proc/inode.c:310 call_read_iter include/linux/fs.h:1969 [inline] new_sync_read+0x41e/0x6e0 fs/read_write.c:415 vfs_read+0x35c/0x570 fs/read_write.c:496 ksys_read+0x12d/0x250 fs/read_write.c:634 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #3 (&p->lock){+.+.}-{3:3}: __mutex_lock_common kernel/locking/mutex.c:952 [inline] __mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1099 seq_read_iter+0xdf/0x1220 fs/seq_file.c:179 call_read_iter include/linux/fs.h:1969 [inline] generic_file_splice_read+0x450/0x6c0 fs/splice.c:311 do_splice_to+0x1bf/0x250 fs/splice.c:796 splice_direct_to_actor+0x2c2/0x8c0 fs/splice.c:870 do_splice_direct+0x1b3/0x280 fs/splice.c:979 do_sendfile+0x9f0/0x1110 fs/read_write.c:1260 __do_sys_sendfile64 fs/read_write.c:1325 [inline] __se_sys_sendfile64 fs/read_write.c:1311 [inline] __x64_sys_sendfile64+0x1cc/0x210 fs/read_write.c:1311 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #2 (sb_writers#3){.+.+}-{0:0}: percpu_down_read include/linux/percpu-rwsem.h:51 [inline] __sb_start_write include/linux/fs.h:1638 [inline] sb_start_write include/linux/fs.h:1708 [inline] file_start_write include/linux/fs.h:2891 [inline] lo_write_bvec+0x3ed/0x6c0 drivers/block/loop.c:286 lo_write_simple drivers/block/loop.c:309 [inline] do_req_filebacked drivers/block/loop.c:627 [inline] loop_handle_cmd drivers/block/loop.c:2143 [inline] loop_process_work+0xc60/0x25a0 drivers/block/loop.c:2183 process_one_work+0x98d/0x1600 kernel/workqueue.c:2275 worker_thread+0x64c/0x1120 kernel/workqueue.c:2421 kthread+0x3b1/0x4a0 kernel/kthread.c:292 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 -> #1 ((work_completion)(&worker->work)){+.+.}-{0:0}: process_one_work+0x8fc/0x1600 kernel/workqueue.c:2251 worker_thread+0x64c/0x1120 kernel/workqueue.c:2421 kthread+0x3b1/0x4a0 kernel/kthread.c:292 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 -> #0 ((wq_completion)loop292057088){+.+.}-{0:0}: check_prev_add kernel/locking/lockdep.c:2937 [inline] check_prevs_add kernel/locking/lockdep.c:3060 [inline] validate_chain kernel/locking/lockdep.c:3675 [inline] __lock_acquire+0x2a17/0x5230 kernel/locking/lockdep.c:4901 lock_acquire kernel/locking/lockdep.c:5511 [inline] lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5476 flush_workqueue+0x110/0x13e0 kernel/workqueue.c:2786 drain_workqueue+0x1a5/0x3c0 kernel/workqueue.c:2951 destroy_workqueue+0x71/0x760 kernel/workqueue.c:4382 __loop_clr_fd+0x1f8/0x14a0 drivers/block/loop.c:1296 loop_clr_fd drivers/block/loop.c:1422 [inline] lo_ioctl+0x3b9/0x1620 drivers/block/loop.c:1780 blkdev_ioctl+0x2a1/0x6d0 block/ioctl.c:583 block_ioctl+0xf9/0x140 fs/block_dev.c:1667 vfs_ioctl fs/ioctl.c:48 [inline] __do_sys_ioctl fs/ioctl.c:753 [inline] __se_sys_ioctl fs/ioctl.c:739 [inline] __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xae other info that might help us debug this: Chain exists of: (wq_completion)loop292057088 --> loop_ctl_mutex --> &lo->lo_mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&lo->lo_mutex); lock(loop_ctl_mutex); lock(&lo->lo_mutex); lock((wq_completion)loop292057088); *** DEADLOCK *** 1 lock held by syz-executor.4/13936: #0: ffff88801a730468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x95/0x14a0 drivers/block/loop.c:1278 stack backtrace: CPU: 0 PID: 13936 Comm: syz-executor.4 Not tainted 5.12.0-rc3-next-20210318-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:79 [inline] dump_stack+0x141/0x1d7 lib/dump_stack.c:120 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2128 check_prev_add kernel/locking/lockdep.c:2937 [inline] check_prevs_add kernel/locking/lockdep.c:3060 [inline] validate_chain kernel/locking/lockdep.c:3675 [inline] __lock_acquire+0x2a17/0x5230 kernel/locking/lockdep.c:4901 lock_acquire kernel/locking/lockdep.c:5511 [inline] lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5476 flush_workqueue+0x110/0x13e0 kernel/workqueue.c:2786 drain_workqueue+0x1a5/0x3c0 kernel/workqueue.c:2951 destroy_workqueue+0x71/0x760 kernel/workqueue.c:4382 __loop_clr_fd+0x1f8/0x14a0 drivers/block/loop.c:1296 loop_clr_fd drivers/block/loop.c:1422 [inline] lo_ioctl+0x3b9/0x1620 drivers/block/loop.c:1780 blkdev_ioctl+0x2a1/0x6d0 block/ioctl.c:583 block_ioctl+0xf9/0x140 fs/block_dev.c:1667 vfs_ioctl fs/ioctl.c:48 [inline] __do_sys_ioctl fs/ioctl.c:753 [inline] __se_sys_ioctl fs/ioctl.c:739 [inline] __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x466217 Code: 3c 1c 48 f7 d8 49 39 c4 72 b8 e8 a4 48 02 00 85 c0 78 bd 48 83 c4 08 4c 89 e0 5b 41 5c c3 0f 1f 44 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f4df82a3fa8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000020001600 RCX: 0000000000466217 RDX: 0000000000000000 RSI: 0000000000004c01 RDI: 0000000000000005 RBP: 00007f4df82a46bc R08: 00007f4df82a4040 R09: 0000000020001440 R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff R13: 0000000000000016 R14: 00007f4df82a4000 R15: 0000000020001640 --- This report is generated by a bot. 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