From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koe...@pengutronix.de>
The patch "list_bl.h: make list head locking RT safe" introduced
an unconditional
__set_bit(0, (unsigned long *)b);
in void hlist_bl_lock(struct hlist_bl_head *b). This clobbers the value
of b->first. When the value of b->first is retrieved using
hlist_bl_first the clobbering is undone using
(unsigned long)h->first & ~LIST_BL_LOCKMASK
and so depending on LIST_BL_LOCKMASK being one. But LIST_BL_LOCKMASK is
only one if at least on of CONFIG_SMP and CONFIG_DEBUG_SPINLOCK are
defined. Without these the value returned by hlist_bl_first has the
zeroth bit set which likely results in a crash.
So only do the clobbering in the cases where LIST_BL_LOCKMASK is one.
An alternative would be to always define LIST_BL_LOCKMASK to one with
CONFIG_PREEMPT_RT_BASE.
Cc: stable...@vger.kernel.org
Acked-by: Paul Gortmaker <paul.gortma...@windriver.com>
Tested-by: Paul Gortmaker <paul.gortma...@windriver.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koe...@pengutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
include/linux/list_bl.h | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
index ddfd46a..becd7a6 100644
--- a/include/linux/list_bl.h
+++ b/include/linux/list_bl.h
@@ -131,8 +131,10 @@ static inline void hlist_bl_lock(struct hlist_bl_head *b)
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
}
static inline void hlist_bl_unlock(struct hlist_bl_head *b)
@@ -140,7 +142,9 @@ static inline void hlist_bl_unlock(struct hlist_bl_head *b)
#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
}
--
1.7.10.4
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