On Tue, Jan 08, 2019 at 11:43:19PM -0500, Qian Cai wrote:
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.0.0-rc1+ #60 Not tainted
> ------------------------------------------------------
> read_all/7952 is trying to acquire lock:
> 0000000019f12603 (mem_hotplug_lock.rw_sem){++++}, at: show_slab_objects+0x16c/0x450
>
> but task is already holding lock:
> 000000008804717f (kn->count#69){++++}, at: kernfs_seq_start+0x79/0x170
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #3 (kn->count#69){++++}:
> __lock_acquire+0x728/0x1200
> lock_acquire+0x269/0x5a0
> __kernfs_remove+0x72f/0x9a0
> kernfs_remove_by_name_ns+0x45/0x90
> sysfs_remove_link+0x3c/0xa0
> sysfs_slab_add+0x1bd/0x330
> __kmem_cache_create+0x166/0x1c0
> create_cache+0xcf/0x1f0
> kmem_cache_create_usercopy+0x1aa/0x270
> kmem_cache_create+0x16/0x20
> mlx5_init_fs+0x195/0x1a10 [mlx5_core]
> mlx5_load_one+0x1106/0x1e90 [mlx5_core]
> init_one+0x864/0xd60 [mlx5_core]
> local_pci_probe+0xda/0x190
> work_for_cpu_fn+0x56/0xa0
> process_one_work+0xad7/0x1b80
> worker_thread+0x8ff/0x1370
> kthread+0x32c/0x3f0
> ret_from_fork+0x27/0x50
>
> -> #2 (slab_mutex){+.+.}:
> __lock_acquire+0x728/0x1200
> lock_acquire+0x269/0x5a0
> __mutex_lock+0x168/0x1730
> mutex_lock_nested+0x1b/0x20
> kmem_cache_create_usercopy+0x45/0x270
> kmem_cache_create+0x16/0x20
> ptlock_cache_init+0x24/0x2d
> start_kernel+0x40e/0x7e0
> x86_64_start_reservations+0x24/0x26
> x86_64_start_kernel+0xef/0xf6
> secondary_startup_64+0xb6/0xc0
>
> -> #1 (memcg_cache_ids_sem){++++}:
> ptlock_cache_init+0x24/0x2d
> start_kernel+0x40e/0x7e0
> x86_64_start_reservations+0x24/0x26
> x86_64_start_kernel+0xef/0xf6
> secondary_startup_64+0xb6/0xc0
>
> -> #0 (mem_hotplug_lock.rw_sem){++++}:
> validate_chain.isra.14+0x11af/0x3b50
> __lock_acquire+0x728/0x1200
> lock_acquire+0x269/0x5a0
> get_online_mems+0x3d/0x80
> show_slab_objects+0x16c/0x450
> total_objects_show+0x13/0x20
> slab_attr_show+0x1e/0x30
> sysfs_kf_seq_show+0x1d5/0x470
> kernfs_seq_show+0x1fa/0x2c0
> seq_read+0x3f7/0x1050
> kernfs_fop_read+0x126/0x650
> __vfs_read+0xeb/0xf20
> vfs_read+0x103/0x290
> ksys_read+0xfa/0x260
> __x64_sys_read+0x73/0xb0
> do_syscall_64+0x18f/0xd23
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> other info that might help us debug this:
>
> Chain exists of:
> mem_hotplug_lock.rw_sem --> slab_mutex --> kn->count#69
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> CPU0 CPU1
> ---- ----
> lock(kn->count#69);
> lock(slab_mutex);
> lock(kn->count#69);
> lock(mem_hotplug_lock.rw_sem);
>
>
> 3 locks held by read_all/7952:
> #0: 0000000005c4ddec (&p->lock){+.+.}, at: seq_read+0x6b/0x1050
> #1: 00000000c2f2e854 (&of->mutex){+.+.}, at: kernfs_seq_start+0x4f/0x170
> #2: 000000008804717f (kn->count#69){++++}, at: kernfs_seq_start+0x79/0x170
>
>
You stripped out the stack trace at the bottom that shows the inversion
:/
