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    Subject[PATCH -tip v3 5/7] kprobes/x86: Disable preempt ftrace-based jprobe
    Date
    Disable preempt in ftrace-based jprobe handler as
    described in Documentation/kprobes.txt, there is

    "Probe handlers are run with preemption disabled."

    This will fix jprobes behavior when CONFIG_PREEMPT=y.

    Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
    ---
    arch/x86/kernel/kprobes/ftrace.c | 23 ++++++++++++++---------
    1 file changed, 14 insertions(+), 9 deletions(-)

    diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
    index 041f7b6dfa0f..bcfee4f69b0e 100644
    --- a/arch/x86/kernel/kprobes/ftrace.c
    +++ b/arch/x86/kernel/kprobes/ftrace.c
    @@ -26,7 +26,7 @@
    #include "common.h"

    static nokprobe_inline
    -int __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
    +void __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
    struct kprobe_ctlblk *kcb, unsigned long orig_ip)
    {
    /*
    @@ -41,20 +41,21 @@ int __skip_singlestep(struct kprobe *p, struct pt_regs *regs,
    __this_cpu_write(current_kprobe, NULL);
    if (orig_ip)
    regs->ip = orig_ip;
    - return 1;
    }

    int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
    struct kprobe_ctlblk *kcb)
    {
    - if (kprobe_ftrace(p))
    - return __skip_singlestep(p, regs, kcb, 0);
    - else
    - return 0;
    + if (kprobe_ftrace(p)) {
    + __skip_singlestep(p, regs, kcb, 0);
    + preempt_enable_no_resched();
    + return 1;
    + }
    + return 0;
    }
    NOKPROBE_SYMBOL(skip_singlestep);

    -/* Ftrace callback handler for kprobes */
    +/* Ftrace callback handler for kprobes -- called under preepmt disabed */
    void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
    struct ftrace_ops *ops, struct pt_regs *regs)
    {
    @@ -77,13 +78,17 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
    /* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */
    regs->ip = ip + sizeof(kprobe_opcode_t);

    + /* To emulate trap based kprobes, preempt_disable here */
    + preempt_disable();
    __this_cpu_write(current_kprobe, p);
    kcb->kprobe_status = KPROBE_HIT_ACTIVE;
    - if (!p->pre_handler || !p->pre_handler(p, regs))
    + if (!p->pre_handler || !p->pre_handler(p, regs)) {
    __skip_singlestep(p, regs, kcb, orig_ip);
    + preempt_enable_no_resched();
    + }
    /*
    * If pre_handler returns !0, it sets regs->ip and
    - * resets current kprobe.
    + * resets current kprobe, and keep preempt count +1.
    */
    }
    end:
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