[v5.15] possible deadlock in blk_request_module (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0996e0926f6b Linux 5.15.220
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=121c7749580000
kernel config: https://syzkaller.appspot.com/x/.config?x=21845b39f8fc6be8
dashboard link: https://syzkaller.appspot.com/bug?extid=e875946a5b2fbe0c27e3
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/dc4b8d8e9340/disk-0996e092.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d165c7b0f84a/vmlinux-0996e092.xz
kernel image: https://storage.googleapis.com/syzbot-assets/27adabc89e72/bzImage-0996e092.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e87594...@syzkaller.appspotmail.com

md: array md0 already initialised!
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.3676/19778 is trying to acquire lock:
ffffffff8c90f308 (major_names_lock){+.+.}-{3:3}, at: blk_probe_dev block/genhd.c:682 [inline]
ffffffff8c90f308 (major_names_lock){+.+.}-{3:3}, at: blk_request_module+0x31/0x290 block/genhd.c:698

but task is already holding lock:
ffff8880789742c0 (&mddev->reconfig_mutex){+.+.}-{3:3}, at: mddev_lock drivers/md/md.h:543 [inline]
ffff8880789742c0 (&mddev->reconfig_mutex){+.+.}-{3:3}, at: md_ioctl+0xbc5/0x26f0 drivers/md/md.c:7645

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&mddev->reconfig_mutex){+.+.}-{3:3}:
__mutex_lock_common+0x1e5/0x2400 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_interruptible_nested+0x17/0x20 kernel/locking/mutex.c:765
mddev_lock drivers/md/md.h:543 [inline]
new_dev_store+0x222/0x660 drivers/md/md.c:4664
md_attr_store+0xdd/0x130 drivers/md/md.c:5636
kernfs_fop_write_iter+0x3a8/0x500 fs/kernfs/file.c:296
call_write_iter include/linux/fs.h:2179 [inline]
new_sync_write fs/read_write.c:507 [inline]
vfs_write+0x748/0xd70 fs/read_write.c:594
ksys_write+0x153/0x260 fs/read_write.c:647
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #3 (kn->active#397){++++}-{0:0}:
kernfs_drain fs/kernfs/dir.c:478 [inline]
__kernfs_remove+0x5da/0xcb0 fs/kernfs/dir.c:1372
kernfs_remove+0x1d/0x30 fs/kernfs/dir.c:1406
__kobject_del+0xe0/0x2e0 lib/kobject.c:628
kobject_del+0x41/0x60 lib/kobject.c:651
mddev_delayed_delete+0x27/0x30 drivers/md/md.c:5678
process_one_work+0x867/0xff0 kernel/workqueue.c:2310
worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
kthread+0x42e/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #2 ((work_completion)(&mddev->del_work)){+.+.}-{0:0}:
process_one_work+0x7ba/0xff0 kernel/workqueue.c:2286
worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
kthread+0x42e/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

-> #1 ((wq_completion)md_misc){+.+.}-{0:0}:
flush_workqueue+0x16a/0x1390 kernel/workqueue.c:2830
md_alloc+0x2e/0xc10 drivers/md/md.c:5720
blk_probe_dev block/genhd.c:685 [inline]
blk_request_module+0x26e/0x290 block/genhd.c:-1
blkdev_get_no_open+0x38/0x1d0 block/bdev.c:736
blkdev_get_by_dev+0x77/0xa50 block/bdev.c:803
blkdev_open+0x128/0x2c0 block/fops.c:466
do_dentry_open+0x7f7/0xf90 fs/open.c:826
do_open fs/namei.c:3659 [inline]
path_openat+0x2718/0x2fb0 fs/namei.c:3793
do_filp_open+0x1df/0x400 fs/namei.c:3820
do_sys_openat2+0x14b/0x500 fs/open.c:1255
do_sys_open fs/open.c:1271 [inline]
__do_sys_openat fs/open.c:1287 [inline]
__se_sys_openat fs/open.c:1282 [inline]
__x64_sys_openat+0x135/0x160 fs/open.c:1282
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #0 (major_names_lock){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x2c66/0x7b50 kernel/locking/lockdep.c:5012
lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
__mutex_lock_common+0x1e5/0x2400 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
blk_probe_dev block/genhd.c:682 [inline]
blk_request_module+0x31/0x290 block/genhd.c:698
blkdev_get_no_open+0x38/0x1d0 block/bdev.c:736
blkdev_get_by_dev+0x77/0xa50 block/bdev.c:803
lock_rdev drivers/md/md.c:2576 [inline]
md_import_device+0x3e2/0x810 drivers/md/md.c:3774
md_add_new_disk+0x583/0x1960 drivers/md/md.c:6940
md_ioctl+0x236f/0x26f0 drivers/md/md.c:7770
blkdev_ioctl+0x347/0x6f0 block/ioctl.c:604
block_ioctl+0xac/0xf0 block/fops.c:496
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

Chain exists of:
major_names_lock --> kn->active#397 --> &mddev->reconfig_mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&mddev->reconfig_mutex);
lock(kn->active#397);
lock(&mddev->reconfig_mutex);
lock(major_names_lock);

*** DEADLOCK ***

1 lock held by syz.0.3676/19778:
#0: ffff8880789742c0 (&mddev->reconfig_mutex){+.+.}-{3:3}, at: mddev_lock drivers/md/md.h:543 [inline]
#0: ffff8880789742c0 (&mddev->reconfig_mutex){+.+.}-{3:3}, at: md_ioctl+0xbc5/0x26f0 drivers/md/md.c:7645

stack backtrace:
CPU: 1 PID: 19778 Comm: syz.0.3676 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
check_noncircular+0x296/0x330 kernel/locking/lockdep.c:2133
check_prev_add kernel/locking/lockdep.c:3053 [inline]
check_prevs_add kernel/locking/lockdep.c:3172 [inline]
validate_chain kernel/locking/lockdep.c:3788 [inline]
__lock_acquire+0x2c66/0x7b50 kernel/locking/lockdep.c:5012
lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
__mutex_lock_common+0x1e5/0x2400 kernel/locking/mutex.c:596
__mutex_lock kernel/locking/mutex.c:729 [inline]
mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
blk_probe_dev block/genhd.c:682 [inline]
blk_request_module+0x31/0x290 block/genhd.c:698
blkdev_get_no_open+0x38/0x1d0 block/bdev.c:736
blkdev_get_by_dev+0x77/0xa50 block/bdev.c:803
lock_rdev drivers/md/md.c:2576 [inline]
md_import_device+0x3e2/0x810 drivers/md/md.c:3774
md_add_new_disk+0x583/0x1960 drivers/md/md.c:6940
md_ioctl+0x236f/0x26f0 drivers/md/md.c:7770
blkdev_ioctl+0x347/0x6f0 block/ioctl.c:604
block_ioctl+0xac/0xf0 block/fops.c:496
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f549aa9a159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5498cf2028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f549ad21fa0 RCX: 00007f549aa9a159
RDX: 0000200000000420 RSI: 0000000040140921 RDI: 0000000000000005
RBP: 00007f549ab3103b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f549ad22038 R14: 00007f549ad21fa0 R15: 00007ffe078af918
</TASK>
md: could not open device unknown-block(0,0).
md: error, md_import_device() returned -6


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