[PATCH] kprobes: increment kprobe missed count for multiprobes

When multiple probes are registered at the same address and if due to some
recursion (probe getting triggered within a probe handler), we skip calling
pre_handlers and just increment nmissed field.

The below patch make sure it walks the list for multiple probes case.
Without the below patch we get incorrect results of nmissed count for
multiple probe case.

Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/kprobes.c

@@ -191,7 +191,7 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
 			 */
 			save_previous_kprobe(kcb);
 			set_current_kprobe(p, regs, kcb);
-			p->nmissed++;
+			kprobes_inc_nmissed_count(p);
 			prepare_singlestep(p, regs);
 			kcb->kprobe_status = KPROBE_REENTER;
 			return 1;

arch/ia64/kernel/kprobes.c

@@ -630,7 +630,7 @@ static int __kprobes pre_kprobes_handler(struct die_args *args)
 			 */
 			save_previous_kprobe(kcb);
 			set_current_kprobe(p, kcb);
-			p->nmissed++;
+			kprobes_inc_nmissed_count(p);
 			prepare_ss(p, regs);
 			kcb->kprobe_status = KPROBE_REENTER;
 			return 1;

arch/powerpc/kernel/kprobes.c

@@ -177,7 +177,7 @@ static inline int kprobe_handler(struct pt_regs *regs)
 			save_previous_kprobe(kcb);
 			set_current_kprobe(p, regs, kcb);
 			kcb->kprobe_saved_msr = regs->msr;
-			p->nmissed++;
+			kprobes_inc_nmissed_count(p);
 			prepare_singlestep(p, regs);
 			kcb->kprobe_status = KPROBE_REENTER;
 			return 1;

arch/sparc64/kernel/kprobes.c

@@ -138,7 +138,7 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
 			 */
 			save_previous_kprobe(kcb);
 			set_current_kprobe(p, regs, kcb);
-			p->nmissed++;
+			kprobes_inc_nmissed_count(p);
 			kcb->kprobe_status = KPROBE_REENTER;
 			prepare_singlestep(p, regs, kcb);
 			return 1;

arch/x86_64/kernel/kprobes.c

@@ -329,7 +329,7 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
 				 */
 				save_previous_kprobe(kcb);
 				set_current_kprobe(p, regs, kcb);
-				p->nmissed++;
+				kprobes_inc_nmissed_count(p);
 				prepare_singlestep(p, regs);
 				kcb->kprobe_status = KPROBE_REENTER;
 				return 1;

include/linux/kprobes.h

@@ -158,6 +158,7 @@ extern int arch_init_kprobes(void);
 extern void show_registers(struct pt_regs *regs);
 extern kprobe_opcode_t *get_insn_slot(void);
 extern void free_insn_slot(kprobe_opcode_t *slot);
+extern void kprobes_inc_nmissed_count(struct kprobe *p);
 
 /* Get the kprobe at this addr (if any) - called with preemption disabled */
 struct kprobe *get_kprobe(void *addr);

kernel/kprobes.c

@@ -246,6 +246,19 @@ static int __kprobes aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
 	return ret;
 }
 
+/* Walks the list and increments nmissed count for multiprobe case */
+void __kprobes kprobes_inc_nmissed_count(struct kprobe *p)
+{
+	struct kprobe *kp;
+	if (p->pre_handler != aggr_pre_handler) {
+		p->nmissed++;
+	} else {
+		list_for_each_entry_rcu(kp, &p->list, list)
+			kp->nmissed++;
+	}
+	return;
+}
+
 /* Called with kretprobe_lock held */
 struct kretprobe_instance __kprobes *get_free_rp_inst(struct kretprobe *rp)
 {