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

[Mikulas Patocka <mpatocka@redhat.com>]

On Tue, 12 Nov 2019, Daniel Wagner wrote:

> [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?

Yes - this is intended to be applied to the realtime patchset.

Mikulas

> >  #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
> >  }
> > 
> > --
> > dm-devel mailing list
> > dm-devel@redhat.com
> > https://www.redhat.com/mailman/listinfo/dm-devel
> > 
> 
> Thanks,
> Daniel
>