From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
When compiling the radix tree with -O2, GCC thinks it can optimise:
void *entry = parent->slots[offset];
int siboff = entry - parent->slots;
void *slot = parent->slots + siboff;
into
void *slot = entry;
Unfortunately, 'entry' is a tagged pointer, so this optimisation leads
to getting an unaligned pointer back from radix_tree_lookup_slot().
The test suite wasn't being compiled with optimisation, so we hadn't
spotted it before now. Change the test suite to compile with -O2, and
fix the optimisation problem by passing 'entry' through entry_to_node()
so gcc knows this isn't a plain pointer.
---
lib/radix-tree.c | 3 ++-
tools/testing/radix-tree/Makefile | 2 +-
2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 1b7bf73..8bf1f32 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -105,7 +105,8 @@ static unsigned int radix_tree_descend(struct radix_tree_node *parent,
#ifdef CONFIG_RADIX_TREE_MULTIORDER
if (radix_tree_is_internal_node(entry)) {
- unsigned long siboff = get_slot_offset(parent, entry);
+ unsigned long siboff = get_slot_offset(parent,
+ (void **)entry_to_node(entry));
if (siboff < RADIX_TREE_MAP_SIZE) {
offset = siboff;
entry = rcu_dereference_raw(parent->slots[offset]);
diff --git a/tools/testing/radix-tree/Makefile b/tools/testing/radix-tree/Makefile
index 3b53046..9d0919ed 100644
--- a/tools/testing/radix-tree/Makefile
+++ b/tools/testing/radix-tree/Makefile
@@ -1,5 +1,5 @@
-CFLAGS += -I. -g -Wall -D_LGPL_SOURCE
+CFLAGS += -I. -g -O2 -Wall -D_LGPL_SOURCE
LDFLAGS += -lpthread -lurcu
TARGETS = main
OFILES = main.o radix-tree.o linux.o test.o tag_check.o find_next_bit.o \
--
2.9.3
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