kprobes: Reuse unused kprobe

Reuse unused (waiting for unoptimizing and no user handler)
kprobe on given address instead of returning -EBUSY for
registering a new kprobe.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: 2nddept-manager@sdl.hitachi.co.jp
LKML-Reference: <20101203095416.2961.39080.stgit@ltc236.sdl.hitachi.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 30 insertions, 2 deletions

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index ba4d4c0740cf..134754d18bb4 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -692,6 +692,27 @@ static __kprobes void unoptimize_kprobe(struct kprobe *p, bool force)
         }
 }
 
+/* Cancel unoptimizing for reusing */
+static void reuse_unused_kprobe(struct kprobe *ap)
+{
+        struct optimized_kprobe *op;
+
+        BUG_ON(!kprobe_unused(ap));
+        /*
+         * Unused kprobe MUST be on the way of delayed unoptimizing (means
+         * there is still a relative jump) and disabled.
+         */
+        op = container_of(ap, struct optimized_kprobe, kp);
+        if (unlikely(list_empty(&op->list)))
+                printk(KERN_WARNING "Warning: found a stray unused "
+                        "aggrprobe@%p\n", ap->addr);
+        /* Enable the probe again */
+        ap->flags &= ~KPROBE_FLAG_DISABLED;
+        /* Optimize it again (remove from op->list) */
+        BUG_ON(!kprobe_optready(ap));
+        optimize_kprobe(ap);
+}
+
 /* Remove optimized instructions */
 static void __kprobes kill_optimized_kprobe(struct kprobe *p)
 {
@@ -872,6 +893,13 @@ static void __kprobes __disarm_kprobe(struct kprobe *p, bool reopt)
 #define kprobe_disarmed(p)                      kprobe_disabled(p)
 #define wait_for_kprobe_optimizer()             do {} while (0)
 
+/* There should be no unused kprobes can be reused without optimization */
+static void reuse_unused_kprobe(struct kprobe *ap)
+{
+        printk(KERN_ERR "Error: There should be no unused kprobe here.\n");
+        BUG_ON(kprobe_unused(ap));
+}
+
 static __kprobes void free_aggr_kprobe(struct kprobe *p)
 {
         arch_remove_kprobe(p);
@@ -1173,8 +1201,8 @@ static int __kprobes register_aggr_kprobe(struct kprobe *orig_p,
                         return -ENOMEM;
                 init_aggr_kprobe(ap, orig_p);
         } else if (kprobe_unused(ap))
-                /* Busy to die */
-                return -EBUSY;
+                /* This probe is going to die. Rescue it */
+                reuse_unused_kprobe(ap);
 
         if (kprobe_gone(ap)) {
                 /*