Message-ID: <67eba499.050a0220.297a31.0009.GAE@google.com>
Date: Tue, 01 Apr 2025 01:32:25 -0700
From: syzbot <syzbot+4bb2305559463e8f6a2a@...kaller.appspotmail.com>
To: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com, tj@...nel.org
Subject: [syzbot] [kernfs?] possible deadlock in kernfs_iop_getattr

Hello,

syzbot found the following issue on:

HEAD commit:    acb4f33713b9 Merge tag 'm68knommu-for-v6.15' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=141a064c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dd14976ddc05593f
dashboard link: https://syzkaller.appspot.com/bug?extid=4bb2305559463e8f6a2a
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0a5c59c65f84/disk-acb4f337.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3da19a126568/vmlinux-acb4f337.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b6b972905364/bzImage-acb4f337.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4bb2305559463e8f6a2a@...kaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.14.0-syzkaller-07422-gacb4f33713b9 #0 Not tainted
------------------------------------------------------
syz.2.1091/9434 is trying to acquire lock:
ffff88801bef71e0 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_iop_getattr+0xd3/0x490 fs/kernfs/inode.c:191

but task is already holding lock:
ffff888025395868 (&q->q_usage_counter(io)#19){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:928 [inline]
ffff888025395868 (&q->q_usage_counter(io)#19){++++}-{0:0}, at: loop_change_fd drivers/block/loop.c:643 [inline]
ffff888025395868 (&q->q_usage_counter(io)#19){++++}-{0:0}, at: lo_ioctl+0x203b/0x2850 drivers/block/loop.c:1569

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&q->q_usage_counter(io)#19){++++}-{0:0}:
       lock_acquire+0x116/0x2f0 kernel/locking/lockdep.c:5866
       blk_alloc_queue+0x542/0x620 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4349 [inline]
       __blk_mq_alloc_disk+0x162/0x380 block/blk-mq.c:4396
       loop_add+0x445/0xaf0 drivers/block/loop.c:2067
       loop_init+0x168/0x220 drivers/block/loop.c:2302
       do_one_initcall+0x24a/0x940 init/main.c:1257
       do_initcall_level+0x157/0x210 init/main.c:1319
       do_initcalls+0x71/0xd0 init/main.c:1335
       kernel_init_freeable+0x432/0x5d0 init/main.c:1567
       kernel_init+0x1d/0x2b0 init/main.c:1457
       ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (fs_reclaim){+.+.}-{0:0}:
       lock_acquire+0x116/0x2f0 kernel/locking/lockdep.c:5866
       __fs_reclaim_acquire mm/page_alloc.c:3853 [inline]
       fs_reclaim_acquire+0x88/0x130 mm/page_alloc.c:3867
       might_alloc include/linux/sched/mm.h:318 [inline]
       slab_pre_alloc_hook mm/slub.c:4089 [inline]
       slab_alloc_node mm/slub.c:4167 [inline]
       kmem_cache_alloc_noprof+0x49/0x390 mm/slub.c:4194
       __kernfs_iattrs+0x94/0x280 fs/kernfs/inode.c:37
       kernfs_iattrs fs/kernfs/inode.c:60 [inline]
       __kernfs_setattr fs/kernfs/inode.c:73 [inline]
       kernfs_iop_setattr+0x125/0x410 fs/kernfs/inode.c:127
       notify_change+0xbca/0xe90 fs/attr.c:552
       do_truncate+0x222/0x310 fs/open.c:65
       handle_truncate fs/namei.c:3466 [inline]
       do_open fs/namei.c:3849 [inline]
       path_openat+0x2e4f/0x35d0 fs/namei.c:4004
       do_filp_open+0x284/0x4e0 fs/namei.c:4031
       do_sys_openat2+0x12b/0x1d0 fs/open.c:1429
       do_sys_open fs/open.c:1444 [inline]
       __do_sys_openat fs/open.c:1460 [inline]
       __se_sys_openat fs/open.c:1455 [inline]
       __x64_sys_openat+0x249/0x2a0 fs/open.c:1455
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (iattr_mutex){+.+.}-{4:4}:
       lock_acquire+0x116/0x2f0 kernel/locking/lockdep.c:5866
       __mutex_lock_common kernel/locking/mutex.c:587 [inline]
       __mutex_lock+0x1a5/0x10c0 kernel/locking/mutex.c:732
       __kernfs_iattrs+0x2b/0x280 fs/kernfs/inode.c:32
       kernfs_iattrs fs/kernfs/inode.c:60 [inline]
       __kernfs_setattr fs/kernfs/inode.c:73 [inline]
       kernfs_iop_setattr+0x125/0x410 fs/kernfs/inode.c:127
       notify_change+0xbca/0xe90 fs/attr.c:552
       do_truncate+0x222/0x310 fs/open.c:65
       handle_truncate fs/namei.c:3466 [inline]
       do_open fs/namei.c:3849 [inline]
       path_openat+0x2e4f/0x35d0 fs/namei.c:4004
       do_filp_open+0x284/0x4e0 fs/namei.c:4031
       do_sys_openat2+0x12b/0x1d0 fs/open.c:1429
       do_sys_open fs/open.c:1444 [inline]
       __do_sys_openat fs/open.c:1460 [inline]
       __se_sys_openat fs/open.c:1455 [inline]
       __x64_sys_openat+0x249/0x2a0 fs/open.c:1455
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3166 [inline]
       check_prevs_add kernel/locking/lockdep.c:3285 [inline]
       validate_chain+0xa69/0x24e0 kernel/locking/lockdep.c:3909
       __lock_acquire+0xad5/0xd80 kernel/locking/lockdep.c:5235
       lock_acquire+0x116/0x2f0 kernel/locking/lockdep.c:5866
       down_read+0xb3/0xa50 kernel/locking/rwsem.c:1524
       kernfs_iop_getattr+0xd3/0x490 fs/kernfs/inode.c:191
       loop_query_min_dio_size drivers/block/loop.c:529 [inline]
       loop_assign_backing_file+0x276/0x500 drivers/block/loop.c:582
       loop_change_fd drivers/block/loop.c:645 [inline]
       lo_ioctl+0x20a9/0x2850 drivers/block/loop.c:1569
       blkdev_ioctl+0x5df/0x710 block/ioctl.c:698
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl+0xf1/0x160 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xf3/0x230 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:
  &root->kernfs_iattr_rwsem --> fs_reclaim --> &q->q_usage_counter(io)#19

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&q->q_usage_counter(io)#19);
                               lock(fs_reclaim);
                               lock(&q->q_usage_counter(io)#19);
  rlock(&root->kernfs_iattr_rwsem);

 *** DEADLOCK ***

3 locks held by syz.2.1091/9434:
 #0: ffff8880253ac368 (&lo->lo_mutex){+.+.}-{4:4}, at: loop_global_lock_killable drivers/block/loop.c:118 [inline]
 #0: ffff8880253ac368 (&lo->lo_mutex){+.+.}-{4:4}, at: loop_change_fd drivers/block/loop.c:610 [inline]
 #0: ffff8880253ac368 (&lo->lo_mutex){+.+.}-{4:4}, at: lo_ioctl+0x135f/0x2850 drivers/block/loop.c:1569
 #1: ffff888025395868 (&q->q_usage_counter(io)#19){++++}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:928 [inline]
 #1: ffff888025395868 (&q->q_usage_counter(io)#19){++++}-{0:0}, at: loop_change_fd drivers/block/loop.c:643 [inline]
 #1: ffff888025395868 (&q->q_usage_counter(io)#19){++++}-{0:0}, at: lo_ioctl+0x203b/0x2850 drivers/block/loop.c:1569
 #2: ffff8880253958a0 (&q->q_usage_counter(queue)#20){+.+.}-{0:0}, at: blk_mq_freeze_queue include/linux/blk-mq.h:928 [inline]
 #2: ffff8880253958a0 (&q->q_usage_counter(queue)#20){+.+.}-{0:0}, at: loop_change_fd drivers/block/loop.c:643 [inline]
 #2: ffff8880253958a0 (&q->q_usage_counter(queue)#20){+.+.}-{0:0}, at: lo_ioctl+0x203b/0x2850 drivers/block/loop.c:1569

stack backtrace:
CPU: 0 UID: 0 PID: 9434 Comm: syz.2.1091 Not tainted 6.14.0-syzkaller-07422-gacb4f33713b9 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2079
 check_noncircular+0x142/0x160 kernel/locking/lockdep.c:2211
 check_prev_add kernel/locking/lockdep.c:3166 [inline]
 check_prevs_add kernel/locking/lockdep.c:3285 [inline]
 validate_chain+0xa69/0x24e0 kernel/locking/lockdep.c:3909
 __lock_acquire+0xad5/0xd80 kernel/locking/lockdep.c:5235
 lock_acquire+0x116/0x2f0 kernel/locking/lockdep.c:5866
 down_read+0xb3/0xa50 kernel/locking/rwsem.c:1524
 kernfs_iop_getattr+0xd3/0x490 fs/kernfs/inode.c:191
 loop_query_min_dio_size drivers/block/loop.c:529 [inline]
 loop_assign_backing_file+0x276/0x500 drivers/block/loop.c:582
 loop_change_fd drivers/block/loop.c:645 [inline]
 lo_ioctl+0x20a9/0x2850 drivers/block/loop.c:1569
 blkdev_ioctl+0x5df/0x710 block/ioctl.c:698
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xf1/0x160 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f110418d169
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f1101fd5038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f11043a6080 RCX: 00007f110418d169
RDX: 0000000000000005 RSI: 0000000000004c06 RDI: 0000000000000004
RBP: 00007f110420e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 00007f11043a6080 R15: 00007f11044cfa28
 </TASK>


---
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