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    Subject[PATCH -tip v8 02/26] kprobes/x86: Allow to handle reentered kprobe on singlestepping
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    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@hitachi.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: "H. Peter Anvin" <hpa@zytor.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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