[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>

7 files changed, 19 insertions, 5 deletions

diff --git a/arch/i386/kernel/kprobes.c b/arch/i386/kernel/kprobes.c
index 32b0c24ab9a..19edcd526ba 100644
--- a/arch/i386/kernel/kprobes.c
+++ b/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;
diff --git a/arch/ia64/kernel/kprobes.c b/arch/ia64/kernel/kprobes.c
index 2895d6e6062..89a70400c4f 100644
--- a/arch/ia64/kernel/kprobes.c
+++ b/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;
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 511af54e623..5368f9c2e6b 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/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;
diff --git a/arch/sparc64/kernel/kprobes.c b/arch/sparc64/kernel/kprobes.c
index 96bd09b098f..a97b0f0727a 100644
--- a/arch/sparc64/kernel/kprobes.c
+++ b/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;
diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
index dddeb678b44..afe11f4fbd1 100644
--- a/arch/x86_64/kernel/kprobes.c
+++ b/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;
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 434ecfd7cf4..c03f2dc933d 100644
--- a/include/linux/kprobes.h
+++ b/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);
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index e4f0fc62bd3..3bb71e63a37 100644
--- a/kernel/kprobes.c
+++ b/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)
 {