[tip:perf/kprobes] kprobes/x86: Allow to handle reentered kprobe on single-stepping

[tip-bot for Masami Hiramatsu]

Commit-ID:  6a5022a56ac37da7bffece043331a101ed0040b1
Gitweb:     http://git.kernel.org/tip/6a5022a56ac37da7bffece043331a101ed0040b1
Author:     Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
AuthorDate: Thu, 17 Apr 2014 17:16:51 +0900
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 24 Apr 2014 10:02:55 +0200

kprobes/x86: Allow to handle reentered kprobe on single-stepping

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@xxxxxxxxxxx>
Reviewed-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Jiri Kosina <jkosina@xxxxxxx>
Cc: Jonathan Lebon <jlebon@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20140417081651.26341.10593.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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 61b17dc..da7bdaa 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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