Kprobes: print details of kretprobe on assertion failure

In certain cases like when the real return address can't be found or when
the number of tracked calls to a kretprobed function is less than the
number of returns, we may not be able to find the correct return address
after processing a kretprobe.  Currently we just do a BUG_ON, but no
information is provided about the actual failing kretprobe.

Print out details of the kretprobe before calling BUG().
Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: Maneesh Soni <maneesh@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/i386/kernel/kprobes.c

@@ -449,8 +449,7 @@ fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)
 			break;
 	}
 
-	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
-
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
 	spin_unlock_irqrestore(&kretprobe_lock, flags);
 
 	hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {

arch/ia64/kernel/kprobes.c

@@ -444,7 +444,8 @@ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 			break;
 	}
 
-	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
+
 	regs->cr_iip = orig_ret_address;
 
 	reset_current_kprobe();

arch/powerpc/kernel/kprobes.c

@@ -336,7 +336,7 @@ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 			break;
 	}
 
-	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
 	regs->nip = orig_ret_address;
 
 	reset_current_kprobe();

arch/x86_64/kernel/kprobes.c

@@ -447,7 +447,7 @@ int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 			break;
 	}
 
-	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
 	regs->rip = orig_ret_address;
 
 	reset_current_kprobe();

include/linux/kprobes.h

@@ -157,6 +157,16 @@ struct kretprobe_instance {
 	struct task_struct *task;
 };
 
+static inline void kretprobe_assert(struct kretprobe_instance *ri,
+	unsigned long orig_ret_address, unsigned long trampoline_address)
+{
+	if (!orig_ret_address || (orig_ret_address == trampoline_address)) {
+		printk("kretprobe BUG!: Processing kretprobe %p @ %p\n",
+				ri->rp, ri->rp->kp.addr);
+		BUG();
+	}
+}
+
 extern spinlock_t kretprobe_lock;
 extern struct mutex kprobe_mutex;
 extern int arch_prepare_kprobe(struct kprobe *p);