On Thu, Sep 22, 2016 at 9:53 PM, Matthew Wilcox <mawilcox@xxxxxxxxxxxxxxxxx> wrote: > 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)); As I see this is the only place where get_slot_offset used for unaligned pointer. Nobody uses "multiorder entries" so this never happens. And I have plan to kill this code. > 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 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>