[PATCH] static_key: WARN on usage before jump_label_init was called
From: Hannes Frederic Sowa
Date: Sun Oct 06 2013 - 14:29:25 EST
On Sun, Oct 06, 2013 at 02:12:47AM +0200, Hannes Frederic Sowa wrote:
> On Sat, Oct 05, 2013 at 08:05:58PM -0400, Steven Rostedt wrote:
> > > if (type == JUMP_LABEL_ENABLE) {
> > > - /*
> > > - * We are enabling this jump label. If it is not a nop
> > > - * then something must have gone wrong.
> > > - */
> > > - if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0))
> > > - bug_at((void *)entry->code, __LINE__);
> > > + if (init) {
> > > + /*
> > > + * Jump label is enabled for the first time.
> > > + * So we expect a default_nop...
> > > + */
> > > + if (unlikely(memcmp((void *)entry->code, default_nop, 5)
> > > + != 0))
> > > + bug_at((void *)entry->code, __LINE__);
> > > + } else {
> > > + /*
> > > + * ...otherwise expect an ideal_nop. Otherwise
> > > + * something went horribly wrong.
> > > + */
> > > + if (unlikely(memcmp((void *)entry->code, ideal_nop, 5)
> > > + != 0))
> > > + bug_at((void *)entry->code, __LINE__);
> > > + }
> >
> > I don't know if I like this change. This is similar to a bug we had
> > with the Xen folks, where they didn't realize that jump labels are not
> > suppose to be used (or set) before jump_label_init() is called.
> >
> > I'll have to take a deeper look at this on Monday.
>
> Yes, I understand and saw the commit to call jump_label_init
> earlier. Maybe the default could be to insert illegal instructions by
> default if we try to replace them with nops or branches afterwards anyway.
This would not help, but maybe someting like this patch. Andi Kleen
also recently posted something similar, I cleaned it up a bit.
[PATCH] static_key: WARN on usage before jump_label_init was called
Based on a patch from Andi Kleen.
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Signed-off-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
---
include/linux/jump_label.h | 11 +++++++++++
include/linux/jump_label_ratelimit.h | 2 ++
kernel/jump_label.c | 5 +++++
lib/Makefile | 2 +-
lib/jump_label_initialized.c | 6 ++++++
5 files changed, 25 insertions(+), 1 deletion(-)
create mode 100644 lib/jump_label_initialized.c
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index a507907..ed3a4bd 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -48,6 +48,14 @@
#include <linux/types.h>
#include <linux/compiler.h>
+#include <linux/bug.h>
+
+extern bool static_key_initialized;
+
+#define STATIC_KEY_CHECK_USE() do { \
+ WARN(!static_key_initialized, "%s used before call to jump_label_init", \
+ __func__); \
+} while (0)
#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
@@ -128,6 +136,7 @@ struct static_key {
static __always_inline void jump_label_init(void)
{
+ static_key_initialized = true;
}
static __always_inline bool static_key_false(struct static_key *key)
@@ -146,11 +155,13 @@ static __always_inline bool static_key_true(struct static_key *key)
static inline void static_key_slow_inc(struct static_key *key)
{
+ STATIC_KEY_CHECK_USE();
atomic_inc(&key->enabled);
}
static inline void static_key_slow_dec(struct static_key *key)
{
+ STATIC_KEY_CHECK_USE();
atomic_dec(&key->enabled);
}
diff --git a/include/linux/jump_label_ratelimit.h b/include/linux/jump_label_ratelimit.h
index 1137883..089f70f 100644
--- a/include/linux/jump_label_ratelimit.h
+++ b/include/linux/jump_label_ratelimit.h
@@ -23,12 +23,14 @@ struct static_key_deferred {
};
static inline void static_key_slow_dec_deferred(struct static_key_deferred *key)
{
+ STATIC_KEY_CHECK_USE();
static_key_slow_dec(&key->key);
}
static inline void
jump_label_rate_limit(struct static_key_deferred *key,
unsigned long rl)
{
+ STATIC_KEY_CHECK_USE();
}
#endif /* HAVE_JUMP_LABEL */
#endif /* _LINUX_JUMP_LABEL_RATELIMIT_H */
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 297a924..9019f15 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -58,6 +58,7 @@ static void jump_label_update(struct static_key *key, int enable);
void static_key_slow_inc(struct static_key *key)
{
+ STATIC_KEY_CHECK_USE();
if (atomic_inc_not_zero(&key->enabled))
return;
@@ -103,12 +104,14 @@ static void jump_label_update_timeout(struct work_struct *work)
void static_key_slow_dec(struct static_key *key)
{
+ STATIC_KEY_CHECK_USE();
__static_key_slow_dec(key, 0, NULL);
}
EXPORT_SYMBOL_GPL(static_key_slow_dec);
void static_key_slow_dec_deferred(struct static_key_deferred *key)
{
+ STATIC_KEY_CHECK_USE();
__static_key_slow_dec(&key->key, key->timeout, &key->work);
}
EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
@@ -116,6 +119,7 @@ EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
void jump_label_rate_limit(struct static_key_deferred *key,
unsigned long rl)
{
+ STATIC_KEY_CHECK_USE();
key->timeout = rl;
INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
}
@@ -212,6 +216,7 @@ void __init jump_label_init(void)
key->next = NULL;
#endif
}
+ static_key_initialized = true;
jump_label_unlock();
}
diff --git a/lib/Makefile b/lib/Makefile
index f3bb2cb..7f48ddc 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -26,7 +26,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
gcd.o lcm.o list_sort.o uuid.o flex_array.o iovec.o clz_ctz.o \
bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o \
- percpu_ida.o
+ percpu_ida.o jump_label_initialized.o
obj-y += string_helpers.o
obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
obj-y += kstrtox.o
diff --git a/lib/jump_label_initialized.c b/lib/jump_label_initialized.c
new file mode 100644
index 0000000..a668a40
--- /dev/null
+++ b/lib/jump_label_initialized.c
@@ -0,0 +1,6 @@
+#include <linux/types.h>
+#include <linux/cache.h>
+
+bool static_key_initialized __read_mostly = false;
+EXPORT_SYMBOL_GPL(static_key_initialized);
+
--
1.8.3.1
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