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 > @@ -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 > } >
