Re: [dm-devel] [PATCH 2/2] realtime: avoid BUG when the list is not locked

[Daniel Wagner <dwagner@suse.de>]

[cc: linux-user-rt, Thomas and Sebastian]

On Mon, Nov 11, 2019 at 08:59:44AM -0500, Mikulas Patocka wrote:
> list_bl.h would crash with BUG() if we used it without locking. 
> dm-snapshot uses its own locking on readltime kernels, so to avoid this 
> BUG, we must set LIST_BL_LOCKMASK = 0.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> 
> Index: linux-rt-devel/include/linux/list_bl.h
> ===================================================================
> --- linux-rt-devel.orig/include/linux/list_bl.h	2019-11-07 14:01:51.000000000 +0100
> +++ linux-rt-devel/include/linux/list_bl.h	2019-11-08 10:12:49.000000000 +0100
> @@ -19,7 +19,7 @@
>   * some fast and compact auxiliary data.
>   */
>  
> -#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
> +#if (defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)) && !defined(CONFIG_PREEMPT_RT_BASE)

CONFIG_PREEMPT_RT_BASE is only available in the out of tree -rt patch
set, therefore I assume it's not for mainline, right?

>  #define LIST_BL_LOCKMASK	1UL
>  #else
>  #define LIST_BL_LOCKMASK	0UL
> @@ -161,9 +161,6 @@ static inline void hlist_bl_lock(struct
>  	bit_spin_lock(0, (unsigned long *)b);
>  #else
>  	raw_spin_lock(&b->lock);
> -#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
> -	__set_bit(0, (unsigned long *)b);
> -#endif
>  #endif
>  }
>  
> @@ -172,9 +169,6 @@ static inline void hlist_bl_unlock(struc
>  #ifndef CONFIG_PREEMPT_RT_BASE
>  	__bit_spin_unlock(0, (unsigned long *)b);
>  #else
> -#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
> -	__clear_bit(0, (unsigned long *)b);
> -#endif
>  	raw_spin_unlock(&b->lock);
>  #endif
>  }
> 
> --
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> 

Thanks,
Daniel