jump label: Fix deadlock b/w jump_label_mutex vs. text_mutex

register_kprobe() downs the 'text_mutex' and then calls
jump_label_text_reserved(), which downs the 'jump_label_mutex'.
However, the jump label code takes those mutexes in the reverse
order.

Fix by requiring the caller of jump_label_text_reserved() to do
the jump label locking via the newly added: jump_label_lock(),
jump_label_unlock(). Currently, kprobes is the only user
of jump_label_text_reserved().

Reported-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
LKML-Reference: <759032c48d5e30c27f0bba003d09bffa8e9f28bb.1285965957.git.jbaron@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 99865c33a60d..9437e14f36bd 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1146,13 +1146,16 @@ int __kprobes register_kprobe(struct kprobe *p)
                 return ret;
 
         preempt_disable();
+        jump_label_lock();
         if (!kernel_text_address((unsigned long) p->addr) ||
             in_kprobes_functions((unsigned long) p->addr) ||
             ftrace_text_reserved(p->addr, p->addr) ||
             jump_label_text_reserved(p->addr, p->addr)) {
                 preempt_enable();
+                jump_label_unlock();
                 return -EINVAL;
         }
+        jump_label_unlock();
 
         /* User can pass only KPROBE_FLAG_DISABLED to register_kprobe */
         p->flags &= KPROBE_FLAG_DISABLED;
@@ -1187,6 +1190,8 @@ int __kprobes register_kprobe(struct kprobe *p)
         INIT_LIST_HEAD(&p->list);
         mutex_lock(&kprobe_mutex);
 
+        jump_label_lock(); /* needed to call jump_label_text_reserved() */
+
         get_online_cpus();      /* For avoiding text_mutex deadlock. */
         mutex_lock(&text_mutex);
 
@@ -1214,6 +1219,7 @@ int __kprobes register_kprobe(struct kprobe *p)
 out:
         mutex_unlock(&text_mutex);
         put_online_cpus();
+        jump_label_unlock();
         mutex_unlock(&kprobe_mutex);
 
         if (probed_mod)