[BUG][PATCH] Kprobes - Increment kprobe missed count for multiprobes

[BUG][PATCH] Kprobes - Increment kprobe missed count for multiprobes

[Keshavamurthy Anil S]

[BUG][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>
-----------------------------------------------------
 arch/i386/kernel/kprobes.c    |    2 +-
 arch/ia64/kernel/kprobes.c    |    2 +-
 arch/powerpc/kernel/kprobes.c |    2 +-
 arch/sparc64/kernel/kprobes.c |    2 +-
 arch/x86_64/kernel/kprobes.c  |    2 +-
 include/linux/kprobes.h       |    1 +
 kernel/kprobes.c              |   13 +++++++++++++
 7 files changed, 19 insertions(+), 5 deletions(-)

Index: linux-2.6.15-rc5-mm1/arch/i386/kernel/kprobes.c
===================================================================
--- linux-2.6.15-rc5-mm1.orig/arch/i386/kernel/kprobes.c
+++ linux-2.6.15-rc5-mm1/arch/i386/kernel/kprobes.c
@@ -191,7 +191,7 @@ static int __kprobes kprobe_handler(stru
 			 */
 			save_previous_kprobe(kcb);
 			set_current_kprobe(p, regs, kcb);
-			p->nmissed++;
+			inc_nmissed_count(p);
 			prepare_singlestep(p, regs);
 			kcb->kprobe_status = KPROBE_REENTER;
 			return 1;
Index: linux-2.6.15-rc5-mm1/arch/ia64/kernel/kprobes.c
===================================================================
--- linux-2.6.15-rc5-mm1.orig/arch/ia64/kernel/kprobes.c
+++ linux-2.6.15-rc5-mm1/arch/ia64/kernel/kprobes.c
@@ -630,7 +630,7 @@ static int __kprobes pre_kprobes_handler
 			 */
 			save_previous_kprobe(kcb);
 			set_current_kprobe(p, kcb);
-			p->nmissed++;
+			inc_nmissed_count(p);
 			prepare_ss(p, regs);
 			kcb->kprobe_status = KPROBE_REENTER;
 			return 1;
Index: linux-2.6.15-rc5-mm1/arch/powerpc/kernel/kprobes.c
===================================================================
--- linux-2.6.15-rc5-mm1.orig/arch/powerpc/kernel/kprobes.c
+++ linux-2.6.15-rc5-mm1/arch/powerpc/kernel/kprobes.c
@@ -174,7 +174,7 @@ static inline int kprobe_handler(struct 
 			save_previous_kprobe(kcb);
 			set_current_kprobe(p, regs, kcb);
 			kcb->kprobe_saved_msr = regs->msr;
-			p->nmissed++;
+			inc_nmissed_count(p);
 			prepare_singlestep(p, regs);
 			kcb->kprobe_status = KPROBE_REENTER;
 			return 1;
Index: linux-2.6.15-rc5-mm1/arch/sparc64/kernel/kprobes.c
===================================================================
--- linux-2.6.15-rc5-mm1.orig/arch/sparc64/kernel/kprobes.c
+++ linux-2.6.15-rc5-mm1/arch/sparc64/kernel/kprobes.c
@@ -138,7 +138,7 @@ static int __kprobes kprobe_handler(stru
 			 */
 			save_previous_kprobe(kcb);
 			set_current_kprobe(p, regs, kcb);
-			p->nmissed++;
+			inc_nmissed_count(p);
 			kcb->kprobe_status = KPROBE_REENTER;
 			prepare_singlestep(p, regs, kcb);
 			return 1;
Index: linux-2.6.15-rc5-mm1/arch/x86_64/kernel/kprobes.c
===================================================================
--- linux-2.6.15-rc5-mm1.orig/arch/x86_64/kernel/kprobes.c
+++ linux-2.6.15-rc5-mm1/arch/x86_64/kernel/kprobes.c
@@ -329,7 +329,7 @@ int __kprobes kprobe_handler(struct pt_r
 				 */
 				save_previous_kprobe(kcb);
 				set_current_kprobe(p, regs, kcb);
-				p->nmissed++;
+				inc_nmissed_count(p);
 				prepare_singlestep(p, regs);
 				kcb->kprobe_status = KPROBE_REENTER;
 				return 1;
Index: linux-2.6.15-rc5-mm1/include/linux/kprobes.h
===================================================================
--- linux-2.6.15-rc5-mm1.orig/include/linux/kprobes.h
+++ linux-2.6.15-rc5-mm1/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 inc_nmissed_count(struct kprobe *p);
 
 /* Get the kprobe at this addr (if any) - called with preemption disabled */
 struct kprobe *get_kprobe(void *addr);
Index: linux-2.6.15-rc5-mm1/kernel/kprobes.c
===================================================================
--- linux-2.6.15-rc5-mm1.orig/kernel/kprobes.c
+++ linux-2.6.15-rc5-mm1/kernel/kprobes.c
@@ -246,6 +246,19 @@ static int __kprobes aggr_break_handler(
 	return ret;
 }
 
+/* Walks the list and increments nmissed count for multiprobe case */
+void __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)
 {

Re: [BUG][PATCH] Kprobes - Increment kprobe missed count for multiprobes

[Andrew Morton]

Keshavamurthy Anil S <anil.s.keshavamurthy@intel.com> wrote:
>
>  +void __kprobes inc_nmissed_count(struct kprobe *p)

That's not a good name for a global identifier.  I renamed it to
kprobes_inc_nmissed_count().

RE: [BUG][PATCH] Kprobes - Increment kprobe missed count for multiprobes

[Keshavamurthy, Anil S]

Sounds good. I should have done a better job. Any way thanks Andrew.

-Anil Keshavamurthy

>-----Original Message-----
>From: Andrew Morton [mailto:akpm@osdl.org] 
>Sent: Saturday, December 10, 2005 12:15 AM
>To: Keshavamurthy, Anil S
>Cc: linux-kernel@vger.kernel.org; ananth@in.ibm.com; 
>prasanna@in.ibm.com
>Subject: Re: [BUG][PATCH] Kprobes - Increment kprobe missed 
>count for multiprobes
>
>Keshavamurthy Anil S <anil.s.keshavamurthy@intel.com> wrote:
>>
>>  +void __kprobes inc_nmissed_count(struct kprobe *p)
>
>That's not a good name for a global identifier.  I renamed it to
>kprobes_inc_nmissed_count().
>