* [PATCH RT 2/2 v2] list_bl: avoid BUG when the list is not locked
@ 2019-11-12 16:16 Mikulas Patocka
2019-11-13 10:29 ` Nikos Tsironis
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: Mikulas Patocka @ 2019-11-12 16:16 UTC (permalink / raw)
To: tglx, linux-rt-users
Cc: Mike Snitzer, Nikos Tsironis, Scott Wood, Ilias Tsitsimpis,
dm-devel, linux-kernel, linux-fsdevel, Daniel Wagner,
Sebastian Andrzej Siewior
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@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)
#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
}
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH RT 2/2 v2] list_bl: avoid BUG when the list is not locked 2019-11-12 16:16 [PATCH RT 2/2 v2] list_bl: avoid BUG when the list is not locked Mikulas Patocka @ 2019-11-13 10:29 ` Nikos Tsironis 2019-11-13 11:16 ` Mikulas Patocka 2019-11-13 11:18 ` [PATCH RT 2/2 v3] " Mikulas Patocka 2019-11-13 13:10 ` [PATCH RT 2/2 v4] " Nikos Tsironis 2 siblings, 1 reply; 7+ messages in thread From: Nikos Tsironis @ 2019-11-13 10:29 UTC (permalink / raw) To: Mikulas Patocka, tglx, linux-rt-users Cc: Mike Snitzer, Scott Wood, Ilias Tsitsimpis, dm-devel, linux-kernel, linux-fsdevel, Daniel Wagner, Sebastian Andrzej Siewior 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@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) > #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 > } > ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH RT 2/2 v2] list_bl: avoid BUG when the list is not locked 2019-11-13 10:29 ` Nikos Tsironis @ 2019-11-13 11:16 ` Mikulas Patocka 2019-11-13 11:50 ` Nikos Tsironis 0 siblings, 1 reply; 7+ messages in thread From: Mikulas Patocka @ 2019-11-13 11:16 UTC (permalink / raw) To: Nikos Tsironis Cc: tglx, linux-rt-users, Mike Snitzer, Scott Wood, Ilias Tsitsimpis, dm-devel, linux-kernel, linux-fsdevel, Daniel Wagner, Sebastian Andrzej Siewior 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@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) > > #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 > > } > > > ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH RT 2/2 v2] list_bl: avoid BUG when the list is not locked 2019-11-13 11:16 ` Mikulas Patocka @ 2019-11-13 11:50 ` Nikos Tsironis 2019-11-13 12:05 ` Mikulas Patocka 0 siblings, 1 reply; 7+ messages in thread From: Nikos Tsironis @ 2019-11-13 11:50 UTC (permalink / raw) To: Mikulas Patocka Cc: tglx, linux-rt-users, Mike Snitzer, Scott Wood, Ilias Tsitsimpis, dm-devel, linux-kernel, linux-fsdevel, Daniel Wagner, Sebastian Andrzej Siewior On 11/13/19 1:16 PM, Mikulas Patocka wrote: > > > 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@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) >>> #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. > I think this causes another problem. LIST_BL_LOCKMASK is used in various functions to set/clear the lock bit, e.g. in hlist_bl_first(). So, if we lock the list through hlist_bl_lock(), thus setting the lock bit with __set_bit(), and then call hlist_bl_first() to get the first element, the returned pointer will be invalid. As LIST_BL_LOCKMASK is zero the least significant bit of the pointer will be 1. I think for dm-snapshot to work using its own locking, and without list_bl complaining, the following is sufficient: --- a/include/linux/list_bl.h +++ b/include/linux/list_bl.h @@ -25,7 +25,7 @@ #define LIST_BL_LOCKMASK 0UL #endif -#ifdef CONFIG_DEBUG_LIST +#if defined(CONFIG_DEBUG_LIST) && !defined(CONFIG_PREEMPT_RT_BASE) #define LIST_BL_BUG_ON(x) BUG_ON(x) #else #define LIST_BL_BUG_ON(x) Nikos > 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 >>> } >>> >> > ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH RT 2/2 v2] list_bl: avoid BUG when the list is not locked 2019-11-13 11:50 ` Nikos Tsironis @ 2019-11-13 12:05 ` Mikulas Patocka 0 siblings, 0 replies; 7+ messages in thread From: Mikulas Patocka @ 2019-11-13 12:05 UTC (permalink / raw) To: Nikos Tsironis Cc: tglx, linux-rt-users, Mike Snitzer, Scott Wood, Ilias Tsitsimpis, dm-devel, linux-kernel, linux-fsdevel, Daniel Wagner, Sebastian Andrzej Siewior On Wed, 13 Nov 2019, Nikos Tsironis wrote: > On 11/13/19 1:16 PM, Mikulas Patocka wrote: > > > > > > 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@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) > >>> #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. > > > > I think this causes another problem. LIST_BL_LOCKMASK is used in various > functions to set/clear the lock bit, e.g. in hlist_bl_first(). So, if we > lock the list through hlist_bl_lock(), thus setting the lock bit with > __set_bit(), and then call hlist_bl_first() to get the first element, > the returned pointer will be invalid. As LIST_BL_LOCKMASK is zero the > least significant bit of the pointer will be 1. > > I think for dm-snapshot to work using its own locking, and without > list_bl complaining, the following is sufficient: > > --- a/include/linux/list_bl.h > +++ b/include/linux/list_bl.h > @@ -25,7 +25,7 @@ > #define LIST_BL_LOCKMASK 0UL > #endif > > -#ifdef CONFIG_DEBUG_LIST > +#if defined(CONFIG_DEBUG_LIST) && !defined(CONFIG_PREEMPT_RT_BASE) > #define LIST_BL_BUG_ON(x) BUG_ON(x) > #else > #define LIST_BL_BUG_ON(x) > > Nikos Yes - so, submit this. Reviewed-by: Mikulas Patocka <mpatocka@redhat.com> Mikulas ^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH RT 2/2 v3] list_bl: avoid BUG when the list is not locked 2019-11-12 16:16 [PATCH RT 2/2 v2] list_bl: avoid BUG when the list is not locked Mikulas Patocka 2019-11-13 10:29 ` Nikos Tsironis @ 2019-11-13 11:18 ` Mikulas Patocka 2019-11-13 13:10 ` [PATCH RT 2/2 v4] " Nikos Tsironis 2 siblings, 0 replies; 7+ messages in thread From: Mikulas Patocka @ 2019-11-13 11:18 UTC (permalink / raw) To: tglx, linux-rt-users Cc: Mike Snitzer, Nikos Tsironis, Scott Wood, Ilias Tsitsimpis, dm-devel, linux-kernel, linux-fsdevel, Daniel Wagner, Sebastian Andrzej Siewior 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@redhat.com> --- include/linux/list_bl.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: linux-rt-devel/include/linux/list_bl.h =================================================================== --- linux-rt-devel.orig/include/linux/list_bl.h 2019-11-13 12:15:50.000000000 +0100 +++ linux-rt-devel/include/linux/list_bl.h 2019-11-13 12:15:50.000000000 +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 ^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH RT 2/2 v4] list_bl: avoid BUG when the list is not locked 2019-11-12 16:16 [PATCH RT 2/2 v2] list_bl: avoid BUG when the list is not locked Mikulas Patocka 2019-11-13 10:29 ` Nikos Tsironis 2019-11-13 11:18 ` [PATCH RT 2/2 v3] " Mikulas Patocka @ 2019-11-13 13:10 ` Nikos Tsironis 2 siblings, 0 replies; 7+ messages in thread From: Nikos Tsironis @ 2019-11-13 13:10 UTC (permalink / raw) To: mpatocka, tglx, linux-rt-users, msnitzer, dm-devel, linux-kernel Cc: swood, linux-fsdevel, dwagner, bigeasy, iliastsi, ntsironis 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 deactivate the list debug checks for list_bl on realtime kernels. This patch is intended only for the realtime kernel patchset, not for the upstream kernel. Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com> Reviewed-by: Mikulas Patocka <mpatocka@redhat.com> --- include/linux/list_bl.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h index da38433240f5..3585b2f6b948 100644 --- a/include/linux/list_bl.h +++ b/include/linux/list_bl.h @@ -25,7 +25,7 @@ #define LIST_BL_LOCKMASK 0UL #endif -#ifdef CONFIG_DEBUG_LIST +#if defined(CONFIG_DEBUG_LIST) && !defined(CONFIG_PREEMPT_RT_BASE) #define LIST_BL_BUG_ON(x) BUG_ON(x) #else #define LIST_BL_BUG_ON(x) -- 2.11.0 ^ permalink raw reply related [flat|nested] 7+ messages in thread
end of thread, other threads:[~2019-11-13 13:11 UTC | newest] Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-11-12 16:16 [PATCH RT 2/2 v2] list_bl: avoid BUG when the list is not locked Mikulas Patocka 2019-11-13 10:29 ` Nikos Tsironis 2019-11-13 11:16 ` Mikulas Patocka 2019-11-13 11:50 ` Nikos Tsironis 2019-11-13 12:05 ` Mikulas Patocka 2019-11-13 11:18 ` [PATCH RT 2/2 v3] " Mikulas Patocka 2019-11-13 13:10 ` [PATCH RT 2/2 v4] " Nikos Tsironis
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