[PATCH printk v5 1/1] printk: extend console_lock for per-console locking

[John Ogness]

(Added RANDOM NUMBER DRIVER and KFENCE people.)

Hi Geert,

On 2022-06-08, Geert Uytterhoeven <geert at linux-m68k.org> wrote:
>     =============================
>     [ BUG: Invalid wait context ]
>     5.19.0-rc1-ebisu-00802-g06a0dd60d6e4 #431 Not tainted
>     -----------------------------
>     swapper/0/1 is trying to lock:
>     ffffffc00910bac8 (base_crng.lock){....}-{3:3}, at:
> crng_make_state+0x148/0x1e4
>     other info that might help us debug this:
>     context-{5:5}
>     2 locks held by swapper/0/1:
>      #0: ffffffc008f8ae00 (console_lock){+.+.}-{0:0}, at:
> printk_activate_kthreads+0x10/0x54
>      #1: ffffffc009da4a28 (&meta->lock){....}-{2:2}, at:
> __kfence_alloc+0x378/0x5c4
>     stack backtrace:
>     CPU: 0 PID: 1 Comm: swapper/0 Not tainted
> 5.19.0-rc1-ebisu-00802-g06a0dd60d6e4 #431
>     Hardware name: Renesas Ebisu-4D board based on r8a77990 (DT)
>     Call trace:
>      dump_backtrace.part.0+0x98/0xc0
>      show_stack+0x14/0x28
>      dump_stack_lvl+0xac/0xec
>      dump_stack+0x14/0x2c
>      __lock_acquire+0x388/0x10a0
>      lock_acquire+0x190/0x2c0
>      _raw_spin_lock_irqsave+0x6c/0x94
>      crng_make_state+0x148/0x1e4
>      _get_random_bytes.part.0+0x4c/0xe8
>      get_random_u32+0x4c/0x140
>      __kfence_alloc+0x460/0x5c4
>      kmem_cache_alloc_trace+0x194/0x1dc
>      __kthread_create_on_node+0x5c/0x1a8
>      kthread_create_on_node+0x58/0x7c
>      printk_start_kthread.part.0+0x34/0xa8
>      printk_activate_kthreads+0x4c/0x54
>      do_one_initcall+0xec/0x278
>      kernel_init_freeable+0x11c/0x214
>      kernel_init+0x24/0x124
>      ret_from_fork+0x10/0x20

I am guessing you have CONFIG_PROVE_RAW_LOCK_NESTING enabled?

We are seeing a spinlock (base_crng.lock) taken while holding a
raw_spinlock (meta->lock).

kfence_guarded_alloc()
  raw_spin_trylock_irqsave(&meta->lock, flags)
    prandom_u32_max()
      prandom_u32()
        get_random_u32()
          get_random_bytes()
            _get_random_bytes()
              crng_make_state()
                spin_lock_irqsave(&base_crng.lock, flags);

I expect it is allowed to create kthreads via kthread_run() in
early_initcalls.

John Ogness