kprobes: fix wait_for_kprobe_optimizer()

wait_for_kprobe_optimizer() seems largely broken.  It uses
optimizer_comp which is never re-initialized, so
wait_for_kprobe_optimizer() will never wait for anything once
kprobe_optimizer() finishes all pending jobs for the first time.

Also, aside from completion, delayed_work_pending() is %false once
kprobe_optimizer() starts execution and wait_for_kprobe_optimizer()
won't wait for it.

Reimplement it so that it flushes optimizing_work until
[un]optimizing_lists are empty.  Note that this also makes
optimizing_work execute immediately if someone's waiting for it, which
is the nicer behavior.

Only compile tested.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>

1 files changed, 15 insertions, 8 deletions

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 098f396aa409..f230e81a9db6 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -471,7 +471,6 @@ static LIST_HEAD(unoptimizing_list);
 
 static void kprobe_optimizer(struct work_struct *work);
 static DECLARE_DELAYED_WORK(optimizing_work, kprobe_optimizer);
-static DECLARE_COMPLETION(optimizer_comp);
 #define OPTIMIZE_DELAY 5
 
 /*
@@ -552,8 +551,7 @@ static __kprobes void do_free_cleaned_kprobes(struct list_head *free_list)
 /* Start optimizer after OPTIMIZE_DELAY passed */
 static __kprobes void kick_kprobe_optimizer(void)
 {
-        if (!delayed_work_pending(&optimizing_work))
-                schedule_delayed_work(&optimizing_work, OPTIMIZE_DELAY);
+        schedule_delayed_work(&optimizing_work, OPTIMIZE_DELAY);
 }
 
 /* Kprobe jump optimizer */
@@ -592,16 +590,25 @@ static __kprobes void kprobe_optimizer(struct work_struct *work)
         /* Step 5: Kick optimizer again if needed */
         if (!list_empty(&optimizing_list) || !list_empty(&unoptimizing_list))
                 kick_kprobe_optimizer();
-        else
-                /* Wake up all waiters */
-                complete_all(&optimizer_comp);
 }
 
 /* Wait for completing optimization and unoptimization */
 static __kprobes void wait_for_kprobe_optimizer(void)
 {
-        if (delayed_work_pending(&optimizing_work))
-                wait_for_completion(&optimizer_comp);
+        mutex_lock(&kprobe_mutex);
+
+        while (!list_empty(&optimizing_list) || !list_empty(&unoptimizing_list)) {
+                mutex_unlock(&kprobe_mutex);
+
+                /* this will also make optimizing_work execute immmediately */
+                flush_delayed_work(&optimizing_work);
+                /* @optimizing_work might not have been queued yet, relax */
+                cpu_relax();
+
+                mutex_lock(&kprobe_mutex);
+        }
+
+        mutex_unlock(&kprobe_mutex);
 }
 
 /* Optimize kprobe if p is ready to be optimized */