On Wed, 13 Nov 2019, Nikos Tsironis wrote: > On 11/12/19 6:16 PM, Mikulas Patocka wrote: > > list_bl would crash with BUG() if we used it without locking. dm-snapshot > > uses its own locking on realtime kernels (it can't use list_bl because > > list_bl uses raw spinlock and dm-snapshot takes other non-raw spinlocks > > while holding bl_lock). > > > > To avoid this BUG, we must set LIST_BL_LOCKMASK = 0. > > > > This patch is intended only for the realtime kernel patchset, not for the > > upstream kernel. > > > > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> > > > > 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) > > #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 > > } > > > > Hi Mikulas, > > I think removing __set_bit()/__clear_bit() breaks hlist_bl_is_locked(), > which is used by the RCU variant of list_bl. > > Nikos OK. so I can remove this part of the patch. Mikulas > > @@ -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 > > } > > >
