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    SubjectRe: [PATCH] kprobes,x86: disable irq durinr optimized callback
    (2011/04/26 23:19), Jiri Olsa wrote:
    > On Tue, Apr 26, 2011 at 09:46:25AM -0400, Steven Rostedt wrote:
    >> On Tue, Apr 26, 2011 at 03:01:31PM +0200, Jiri Olsa wrote:
    >>> hi,
    >>>
    >>> attached patch is disabling irqs during optimized callback,
    >>> so we dont miss any in-irq kprobes as missed.
    >>>
    >>> Also I think there's small window where current_kprobe variable
    >>> could be touched in non-safe way, but I was not able to hit
    >>> any issue.
    >>>
    >>> I'm not sure wether this is a bug or if it was intentional to have
    >>> irqs enabled during the pre_handler callback.
    >>
    >> That's not very convincing. Did you see if we actually did miss events.
    >> If that's the case then it is a bug. The conversion to optimizing should
    >> not cause events to be missed.
    >
    > yep, running following:
    >
    > # cd /debug/tracing/
    > # echo "p mutex_unlock" >> kprobe_events
    > # echo "p _raw_spin_lock" >> kprobe_events
    > # echo "p smp_apic_timer_interrupt" >> ./kprobe_events
    > # echo 1 > events/enable
    >
    > makes the optimized kprobes to be missed. They are not missed in
    > same testcase for non-optimized kprobes. I should have mentioned
    > that, sry ;)

    Good catch! that's right! kprobes' int3 automatically disables
    irq, but optimized path doesn't. And that causes unexpected
    event loss.


    >
    >>
    >>
    >>>
    >>> wbr,
    >>> jirka
    >>>
    >>> ---
    >>> Disabling irqs during optimized callback, so we dont miss
    >>> any in-irq kprobes as missed.
    >>>
    >>> Interrupts are also disabled during non-optimized kprobes callbacks.
    >>>
    >>> Signed-off-by: Jiri Olsa <jolsa@redhat.com>
    >>> ---
    >>> arch/x86/kernel/kprobes.c | 3 +++
    >>> 1 files changed, 3 insertions(+), 0 deletions(-)
    >>>
    >>> diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
    >>> index c969fd9..917cb31 100644
    >>> --- a/arch/x86/kernel/kprobes.c
    >>> +++ b/arch/x86/kernel/kprobes.c
    >>> @@ -1183,11 +1183,13 @@ static void __kprobes optimized_callback(struct optimized_kprobe *op,
    >>> struct pt_regs *regs)
    >>> {
    >>> struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
    >>> + unsigned long flags;
    >>>
    >>> /* This is possible if op is under delayed unoptimizing */
    >>> if (kprobe_disabled(&op->kp))
    >>> return;
    >>>
    >>> + local_irq_save(flags);
    >>> preempt_disable();
    >>
    >> No reason to disable preemption if you disabled interrupts.

    Right,

    > ops, missed that.. attaching new patch


    > ---
    > Disabling irqs during optimized callback, so we dont miss
    > any in-irq kprobes as missed.
    >
    > running following:
    >
    > # cd /debug/tracing/
    > # echo "p mutex_unlock" >> kprobe_events
    > # echo "p _raw_spin_lock" >> kprobe_events
    > # echo "p smp_apic_timer_interrupt" >> ./kprobe_events
    > # echo 1 > events/enable
    >
    > makes the optimized kprobes to be missed. None is missed
    > if the kprobe optimatization is disabled.
    >
    > Signed-off-by: Jiri Olsa <jolsa@redhat.com>

    Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>


    Ingo, could you pull this as a bugfix?

    Thank you!


    > ---
    > arch/x86/kernel/kprobes.c | 5 +++--
    > 1 files changed, 3 insertions(+), 2 deletions(-)
    >
    > diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
    > index c969fd9..f1a6244 100644
    > --- a/arch/x86/kernel/kprobes.c
    > +++ b/arch/x86/kernel/kprobes.c
    > @@ -1183,12 +1183,13 @@ static void __kprobes optimized_callback(struct optimized_kprobe *op,
    > struct pt_regs *regs)
    > {
    > struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
    > + unsigned long flags;
    >
    > /* This is possible if op is under delayed unoptimizing */
    > if (kprobe_disabled(&op->kp))
    > return;
    >
    > - preempt_disable();
    > + local_irq_save(flags);
    > if (kprobe_running()) {
    > kprobes_inc_nmissed_count(&op->kp);
    > } else {
    > @@ -1207,7 +1208,7 @@ static void __kprobes optimized_callback(struct optimized_kprobe *op,
    > opt_pre_handler(&op->kp, regs);
    > __this_cpu_write(current_kprobe, NULL);
    > }
    > - preempt_enable_no_resched();
    > + local_irq_restore(flags);
    > }
    >
    > static int __kprobes copy_optimized_instructions(u8 *dest, u8 *src)


    --
    Masami HIRAMATSU
    Software Platform Research Dept. Linux Technology Center
    Hitachi, Ltd., Yokohama Research Laboratory
    E-mail: masami.hiramatsu.pt@hitachi.com


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