[syzbot] possible deadlock in loop_probe

syzbot syzbot+6a8a0d93c91e8fbf2e80 at syzkaller.appspotmail.com
Wed Jun 16 14:18:17 PDT 2021 

Hello,

syzbot found the following issue on:

HEAD commit:    8ecfa36c Merge tag 'riscv-for-linus-5.13-rc6' of git://git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17121304300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=547a5e42ca601229
dashboard link: https://syzkaller.appspot.com/bug?extid=6a8a0d93c91e8fbf2e80
compiler:       Debian clang version 11.0.1-2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17065d1fd00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12de53afd00000

The issue was bisected to:

commit 5befc7c26e5a98cd49789fb1beb52c62bd472dba
Author: Keith Busch <kbusch at kernel.org>
Date:   Wed Mar 24 23:18:05 2021 +0000

    nvme: implement non-mdts command limits

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15e62857d00000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=17e62857d00000
console output: https://syzkaller.appspot.com/x/log.txt?x=13e62857d00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6a8a0d93c91e8fbf2e80 at syzkaller.appspotmail.com
Fixes: 5befc7c26e5a ("nvme: implement non-mdts command limits")

======================================================
WARNING: possible circular locking dependency detected
5.13.0-rc5-syzkaller #0 Not tainted
------------------------------------------------------
systemd-udevd/8445 is trying to acquire lock:
ffffffff8d671688 (loop_ctl_mutex){+.+.}-{3:3}, at: loop_probe+0xe1/0x220 drivers/block/loop.c:2234

but task is already holding lock:
ffffffff8d4db008 (major_names_lock){+.+.}-{3:3}, at: blk_request_module+0x2f/0x1c0 block/genhd.c:680

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (major_names_lock){+.+.}-{3:3}:
       lock_acquire+0x17f/0x720 kernel/locking/lockdep.c:5512
       __mutex_lock_common+0x1bf/0x3100 kernel/locking/mutex.c:959
       __mutex_lock kernel/locking/mutex.c:1104 [inline]
       mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1119
       __register_blkdev+0x2c/0x360 block/genhd.c:223
       register_mtd_blktrans+0x94/0x3d0 drivers/mtd/mtd_blkdevs.c:534
       do_one_initcall+0x1a7/0x400 init/main.c:1249
       do_initcall_level+0x14a/0x1f5 init/main.c:1322
       do_initcalls+0x4b/0x8c init/main.c:1338
       kernel_init_freeable+0x3fd/0x58a init/main.c:1560
       kernel_init+0xd/0x290 init/main.c:1447
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

-> #2 (mtd_table_mutex){+.+.}-{3:3}:
       lock_acquire+0x17f/0x720 kernel/locking/lockdep.c:5512
       __mutex_lock_common+0x1bf/0x3100 kernel/locking/mutex.c:959
       __mutex_lock kernel/locking/mutex.c:1104 [inline]
       mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1119
       blktrans_open+0x61/0x430 drivers/mtd/mtd_blkdevs.c:212
       __blkdev_get+0x293/0xa50 fs/block_dev.c:1311
       blkdev_get_by_dev+0xf9/0x640 fs/block_dev.c:1451
       blkdev_open+0x132/0x2c0 fs/block_dev.c:1546
       do_dentry_open+0x7cb/0x1010 fs/open.c:826
       do_open fs/namei.c:3361 [inline]
       path_openat+0x28e6/0x39b0 fs/namei.c:3494
       do_filp_open+0x221/0x460 fs/namei.c:3521
       do_sys_openat2+0x124/0x460 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+0x221/0x270 fs/open.c:1207
       do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #1 (&bdev->bd_mutex){+.+.}-{3:3}:
       lock_acquire+0x17f/0x720 kernel/locking/lockdep.c:5512
       __mutex_lock_common+0x1bf/0x3100 kernel/locking/mutex.c:959
       __mutex_lock kernel/locking/mutex.c:1104 [inline]
       mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1119
       del_gendisk+0x2ab/0x860 block/genhd.c:610
       loop_remove drivers/block/loop.c:2180 [inline]
       loop_control_ioctl+0x62c/0x770 drivers/block/loop.c:2280
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:1069 [inline]
       __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:1055
       do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (loop_ctl_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:2938 [inline]
       check_prevs_add+0x4f9/0x5b60 kernel/locking/lockdep.c:3061
       validate_chain kernel/locking/lockdep.c:3676 [inline]
       __lock_acquire+0x4307/0x6040 kernel/locking/lockdep.c:4902
       lock_acquire+0x17f/0x720 kernel/locking/lockdep.c:5512
       __mutex_lock_common+0x1bf/0x3100 kernel/locking/mutex.c:959
       __mutex_lock kernel/locking/mutex.c:1104 [inline]
       mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1119
       loop_probe+0xe1/0x220 drivers/block/loop.c:2234
       blk_request_module+0x19d/0x1c0 block/genhd.c:683
       blkdev_get_no_open+0x44/0x1f0 fs/block_dev.c:1374
       blkdev_get_by_dev+0x82/0x640 fs/block_dev.c:1437
       blkdev_open+0x132/0x2c0 fs/block_dev.c:1546
       do_dentry_open+0x7cb/0x1010 fs/open.c:826
       do_open fs/namei.c:3361 [inline]
       path_openat+0x28e6/0x39b0 fs/namei.c:3494
       do_filp_open+0x221/0x460 fs/namei.c:3521
       do_sys_openat2+0x124/0x460 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+0x221/0x270 fs/open.c:1207
       do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
       entry_SYSCALL_64_after_hwframe+0x44/0xae

other info that might help us debug this:

Chain exists of:
  loop_ctl_mutex --> mtd_table_mutex --> major_names_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(major_names_lock);
                               lock(mtd_table_mutex);
                               lock(major_names_lock);
  lock(loop_ctl_mutex);

 *** DEADLOCK ***

1 lock held by systemd-udevd/8445:
 #0: ffffffff8d4db008 (major_names_lock){+.+.}-{3:3}, at: blk_request_module+0x2f/0x1c0 block/genhd.c:680

stack backtrace:
CPU: 1 PID: 8445 Comm: systemd-udevd Not tainted 5.13.0-rc5-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+0x202/0x31e lib/dump_stack.c:120
 print_circular_bug+0xb17/0xdc0 kernel/locking/lockdep.c:2007
 check_noncircular+0x2cc/0x390 kernel/locking/lockdep.c:2129
 check_prev_add kernel/locking/lockdep.c:2938 [inline]
 check_prevs_add+0x4f9/0x5b60 kernel/locking/lockdep.c:3061
 validate_chain kernel/locking/lockdep.c:3676 [inline]
 __lock_acquire+0x4307/0x6040 kernel/locking/lockdep.c:4902
 lock_acquire+0x17f/0x720 kernel/locking/lockdep.c:5512
 __mutex_lock_common+0x1bf/0x3100 kernel/locking/mutex.c:959
 __mutex_lock kernel/locking/mutex.c:1104 [inline]
 mutex_lock_nested+0x1a/0x20 kernel/locking/mutex.c:1119
 loop_probe+0xe1/0x220 drivers/block/loop.c:2234
 blk_request_module+0x19d/0x1c0 block/genhd.c:683
 blkdev_get_no_open+0x44/0x1f0 fs/block_dev.c:1374
 blkdev_get_by_dev+0x82/0x640 fs/block_dev.c:1437
 blkdev_open+0x132/0x2c0 fs/block_dev.c:1546
 do_dentry_open+0x7cb/0x1010 fs/open.c:826
 do_open fs/namei.c:3361 [inline]
 path_openat+0x28e6/0x39b0 fs/namei.c:3494
 do_filp_open+0x221/0x460 fs/namei.c:3521
 do_sys_openat2+0x124/0x460 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+0x221/0x270 fs/open.c:1207
 do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f666c06a840
Code: 73 01 c3 48 8b 0d 68 77 20 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 89 bb 20 00 00 75 10 b8 02 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 1e f6 ff ff 48 89 04 24
RSP: 002b:00007ffc880be598 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 000055dd2c8278f0 RCX: 00007f666c06a840
RDX: 000055dd2c52efe3 RSI: 00000000000a0800 RDI: 000055dd2c827830
RBP: 00007ffc880be710 R08: 000055dd2c52e670 R09: 0000000000000010
R10: 000055dd2c52ed0c R11: 0000000000000246 R12: 00007ffc880be660
R13: 000055dd2c829010 R14: 0000000000000003 R15: 000000000000000e


---
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