[syzbot] [block?] [cgroups?] possible deadlock in blkcg_deactivate_policy (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3708dd948844 Merge tag 'pm-7.2-rc6' of git://git.kernel.or..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11fa7a49580000
kernel config: https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=14254d81dd19ba7d7e41
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/aa997b3eeef4/disk-3708dd94.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1ab7e579d11e/vmlinux-3708dd94.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7038f45d2e15/bzImage-3708dd94.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+14254d...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
syz.9.12466/9015 is trying to acquire lock:
ffff8880283a3bc0 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkcg_deactivate_policy+0x167/0x600 block/blk-cgroup.c:1681

but task is already holding lock:
ffff8880553aa8b8 (&eq->sysfs_lock){+.+.}-{4:4}, at: elevator_exit+0x88/0xf0 block/elevator.c:160

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&eq->sysfs_lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
elevator_exit+0x88/0xf0 block/elevator.c:160
elevator_switch+0x3a7/0x7e0 block/elevator.c:580
elevator_change+0x352/0x530 block/elevator.c:681
elevator_set_none+0x92/0xf0 block/elevator.c:769
blk_unregister_queue+0x178/0x310 block/blk-sysfs.c:1073
__del_gendisk+0x2e3/0xb20 block/genhd.c:739
del_gendisk+0x10e/0x1b0 block/genhd.c:819
loop_remove drivers/block/loop.c:2112 [inline]
loop_control_remove drivers/block/loop.c:2171 [inline]
loop_control_ioctl+0x4f8/0x620 drivers/block/loop.c:2213
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&q->elevator_lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
elevator_change+0x1bc/0x530 block/elevator.c:679
elv_iosched_store+0x3be/0x460 block/elevator.c:826
queue_attr_store+0x25f/0x2f0 block/blk-sysfs.c:906
sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&q->q_usage_counter(io)#17){++++}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
blk_alloc_queue+0x610/0x790 block/blk-core.c:504
blk_mq_alloc_queue+0x174/0x290 block/blk-mq.c:4420
__blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4467
loop_add+0x498/0xb60 drivers/block/loop.c:2041
loop_init+0x1d3/0x200 drivers/block/loop.c:2280
do_one_initcall+0x11d/0x700 init/main.c:1347
do_initcall_level init/main.c:1409 [inline]
do_initcalls init/main.c:1425 [inline]
do_basic_setup init/main.c:1445 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1658
kernel_init+0x1f/0x1e0 init/main.c:1548
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (fs_reclaim){+.+.}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__fs_reclaim_acquire mm/page_alloc.c:4329 [inline]
fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4343
might_alloc include/linux/sched/mm.h:317 [inline]
prepare_alloc_pages+0x166/0x5f0 mm/page_alloc.c:5048
__alloc_frozen_pages_noprof+0x1af/0x2dc0 mm/page_alloc.c:5293
__alloc_pages_noprof+0xb/0x110 mm/page_alloc.c:5338
__alloc_pages_node_noprof include/linux/gfp.h:291 [inline]
alloc_pages_node_noprof include/linux/gfp.h:318 [inline]
pcpu_alloc_pages mm/percpu-vm.c:95 [inline]
pcpu_populate_chunk+0x118/0x990 mm/percpu-vm.c:285
pcpu_alloc_noprof+0x881/0x1ca0 mm/percpu.c:1876
bpf_map_alloc_percpu+0x9a/0xf0 kernel/bpf/syscall.c:584
prealloc_init kernel/bpf/hashtab.c:339 [inline]
htab_map_alloc+0x1054/0x14e0 kernel/bpf/hashtab.c:639
map_create_alloc kernel/bpf/syscall.c:1523 [inline]
map_create+0x874/0x3120 kernel/bpf/syscall.c:1640
__sys_bpf+0x2a6e/0x4e80 kernel/bpf/syscall.c:6395
__do_sys_bpf kernel/bpf/syscall.c:6537 [inline]
__se_sys_bpf kernel/bpf/syscall.c:6534 [inline]
__x64_sys_bpf+0xce/0x140 kernel/bpf/syscall.c:6534
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (pcpu_alloc_mutex){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
pcpu_alloc_noprof+0xe87/0x1ca0 mm/percpu.c:1788
percpu_ref_init+0x37/0x3f0 lib/percpu-refcount.c:72
blkg_alloc+0xf0/0xf80 block/blk-cgroup.c:313
blkg_conf_prep+0x46e/0xf10 block/blk-cgroup.c:873
tg_set_conf.isra.0+0x1ed/0x500 block/blk-throttle.c:1373
cgroup_file_write+0x1e6/0x8a0 kernel/cgroup/cgroup.c:4316
kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x6ac/0x1050 fs/read_write.c:687
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&q->blkcg_mutex){+.+.}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
blkcg_deactivate_policy+0x167/0x600 block/blk-cgroup.c:1681
bfq_exit_queue+0x29d/0x430 block/bfq-iosched.c:7165
blk_mq_exit_sched+0x20e/0x4e0 block/blk-mq-sched.c:702
elevator_exit+0x93/0xf0 block/elevator.c:161
elevator_switch+0x3a7/0x7e0 block/elevator.c:580
elevator_change+0x352/0x530 block/elevator.c:681
elevator_set_none+0x92/0xf0 block/elevator.c:769
blk_unregister_queue+0x178/0x310 block/blk-sysfs.c:1073
__del_gendisk+0x2e3/0xb20 block/genhd.c:739
del_gendisk+0x10e/0x1b0 block/genhd.c:819
loop_remove drivers/block/loop.c:2112 [inline]
loop_control_remove drivers/block/loop.c:2171 [inline]
loop_control_ioctl+0x4f8/0x620 drivers/block/loop.c:2213
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 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:
&q->blkcg_mutex --> &q->elevator_lock --> &eq->sysfs_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&eq->sysfs_lock);
lock(&q->elevator_lock);
lock(&eq->sysfs_lock);
lock(&q->blkcg_mutex);

*** DEADLOCK ***

3 locks held by syz.9.12466/9015:
#0: ffff8880283cc3a0 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0x106/0x1b0 block/genhd.c:818
#1: ffff8880283a3d68 (&q->elevator_lock){+.+.}-{4:4}, at: elevator_change+0x1bc/0x530 block/elevator.c:679
#2: ffff8880553aa8b8 (&eq->sysfs_lock){+.+.}-{4:4}, at: elevator_exit+0x88/0xf0 block/elevator.c:160

stack backtrace:
CPU: 0 UID: 0 PID: 9015 Comm: syz.9.12466 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain kernel/locking/lockdep.c:3908 [inline]
__lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237
lock_acquire kernel/locking/lockdep.c:5868 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
blkcg_deactivate_policy+0x167/0x600 block/blk-cgroup.c:1681
bfq_exit_queue+0x29d/0x430 block/bfq-iosched.c:7165
blk_mq_exit_sched+0x20e/0x4e0 block/blk-mq-sched.c:702
elevator_exit+0x93/0xf0 block/elevator.c:161
elevator_switch+0x3a7/0x7e0 block/elevator.c:580
elevator_change+0x352/0x530 block/elevator.c:681
elevator_set_none+0x92/0xf0 block/elevator.c:769
blk_unregister_queue+0x178/0x310 block/blk-sysfs.c:1073
__del_gendisk+0x2e3/0xb20 block/genhd.c:739
del_gendisk+0x10e/0x1b0 block/genhd.c:819
loop_remove drivers/block/loop.c:2112 [inline]
loop_control_remove drivers/block/loop.c:2171 [inline]
loop_control_ioctl+0x4f8/0x620 drivers/block/loop.c:2213
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl fs/ioctl.c:583 [inline]
__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f266f39e019
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:00007f2670208028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f266f625fa0 RCX: 00007f266f39e019
RDX: 0000000000000000 RSI: 0000000000004c81 RDI: 0000000000000003
RBP: 00007f266f43500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f266f626038 R14: 00007f266f625fa0 R15: 00007ffd3333f748
</TASK>


---
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