linux-kernel - [PATCH -tip 2/2] kprobes/x86: Allow to handle reentered kprobe on singlestepping

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Message-ID: <20140220033929.12285.24492.stgit@ltc230.yrl.intra.hitachi.co.jp>
Date:	Thu, 20 Feb 2014 12:39:29 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	fche@...hat.com, "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH -tip 2/2] kprobes/x86: Allow to handle reentered kprobe on
 singlestepping

Since the NMI handlers(e.g. perf) can interrupt in the
single stepping (or preparing the single stepping, do_debug
etc.), we should consider a kprobe is hit in the NMI
handler. Even in that case, the kprobe is allowed to be
reentered as same as the kprobes hit in kprobe handlers
(KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE).
The real issue will happen when a kprobe hit while another
reentered kprobe is processing (KPROBE_REENTER), because
we already consumed a saved-area for the previous kprobe.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
---
 arch/x86/kernel/kprobes/core.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index b482e96..a9a42fa 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -531,10 +531,11 @@ reenter_kprobe(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb
 	switch (kcb->kprobe_status) {
 	case KPROBE_HIT_SSDONE:
 	case KPROBE_HIT_ACTIVE:
+	case KPROBE_HIT_SS:
 		kprobes_inc_nmissed_count(p);
 		setup_singlestep(p, regs, kcb, 1);
 		break;
-	case KPROBE_HIT_SS:
+	case KPROBE_REENTER:
 		/* A probe has been hit in the codepath leading up to, or just
 		 * after, single-stepping of a probed instruction. This entire
 		 * codepath should strictly reside in .kprobes.text section.


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