Re: [PATCH] mm: avoid slub allocation while holding list_lock

[Kirill A. Shutemov]

On Mon, Sep 09, 2019 at 12:10:16AM -0600, Yu Zhao wrote:
> If we are already under list_lock, don't call kmalloc(). Otherwise we
> will run into deadlock because kmalloc() also tries to grab the same
> lock.
> 
> Instead, allocate pages directly. Given currently page->objects has
> 15 bits, we only need 1 page. We may waste some memory but we only do
> so when slub debug is on.
> 
>   WARNING: possible recursive locking detected
>   --------------------------------------------
>   mount-encrypted/4921 is trying to acquire lock:
>   (&(&n->list_lock)->rlock){-.-.}, at: ___slab_alloc+0x104/0x437
> 
>   but task is already holding lock:
>   (&(&n->list_lock)->rlock){-.-.}, at: __kmem_cache_shutdown+0x81/0x3cb
> 
>   other info that might help us debug this:
>    Possible unsafe locking scenario:
> 
>          CPU0
>          ----
>     lock(&(&n->list_lock)->rlock);
>     lock(&(&n->list_lock)->rlock);
> 
>    *** DEADLOCK ***
> 
> Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>

Looks sane to me:

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

-- 
 Kirill A. Shutemov