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authorRussell King <rmk+kernel@arm.linux.org.uk>2011-01-14 13:12:45 +0000
committerNick Piggin <npiggin@kernel.dk>2011-01-14 13:12:45 +0000
commit32385c7cf60a78375b63afc4f02001df84dfd1a0 (patch)
tree6419ac3c77cb38bac389e5efc59928e01780a2ae /include/linux/list_bl.h
parent3ec762ad8be364c2fadfe0d6b2cc6d4d3b5e1b54 (diff)
downloadlinux-linaro-stable-32385c7cf60a78375b63afc4f02001df84dfd1a0.tar.gz
kernel: fix hlist_bl again
__d_rehash is dereferencing an almost-NULL pointer on my ARM926. CONFIG_SMP=n and CONFIG_DEBUG_SPINLOCK=y. The faulting instruction is: strne r3, [r2, #4] and as can be seen from the register dump below, r2 is 0x00000001, hence the faulting 0x00000005 address. __d_rehash is essentially: spin_lock_bucket(b); entry->d_flags &= ~DCACHE_UNHASHED; hlist_bl_add_head_rcu(&entry->d_hash, &b->head); spin_unlock_bucket(b); which is: bit_spin_lock(0, (unsigned long *)&b->head.first); entry->d_flags &= ~DCACHE_UNHASHED; hlist_bl_add_head_rcu(&entry->d_hash, &b->head); __bit_spin_unlock(0, (unsigned long *)&b->head.first); bit_spin_lock(0, ptr) sets bit 0 of *ptr, in this case b->head.first if CONFIG_SMP or CONFIG_DEBUG_SPINLOCK is set: #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK) while (unlikely(test_and_set_bit_lock(bitnum, addr))) { while (test_bit(bitnum, addr)) { preempt_enable(); cpu_relax(); preempt_disable(); } } #endif So, b->head.first starts off NULL, and becomes a non-NULL (address 1). hlist_bl_add_head_rcu() does this: static inline void hlist_bl_add_head_rcu(struct hlist_bl_node *n, struct hlist_bl_head *h) { first = hlist_bl_first(h); n->next = first; if (first) first->pprev = &n->next; It is the store to first->pprev which is faulting. hlist_bl_first(): static inline struct hlist_bl_node *hlist_bl_first(struct hlist_bl_head *h) { return (struct hlist_bl_node *) ((unsigned long)h->first & ~LIST_BL_LOCKMASK); } but: #if defined(CONFIG_SMP) #define LIST_BL_LOCKMASK 1UL #else #define LIST_BL_LOCKMASK 0UL #endif So, we have one piece of code which sets bit 0 of addresses, and another bit of code which doesn't clear it before dereferencing the pointer if !CONFIG_SMP && CONFIG_DEBUG_SPINLOCK. With the patch below, I can again sucessfully boot the kernel on my Versatile PB/926 platform. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'include/linux/list_bl.h')
-rw-r--r--include/linux/list_bl.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
index b2adbb4b2f73..5bad17d1acde 100644
--- a/include/linux/list_bl.h
+++ b/include/linux/list_bl.h
@@ -16,7 +16,7 @@
* some fast and compact auxiliary data.
*/
-#if defined(CONFIG_SMP)
+#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
#define LIST_BL_LOCKMASK 1UL
#else
#define LIST_BL_LOCKMASK 0UL