On Mon, 23 Oct 2017 22:07:38 +0530
"Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:
> Per Documentation/kprobes.txt, probe handlers need to be invoked with
> preemption disabled. Update optimized_callback() to do so. Also move
> get_kprobe_ctlblk() invocation post preemption disable, since it
> accesses pre-cpu data.
>
> This was not an issue so far since optprobes wasn't selected if
> CONFIG_PREEMPT was enabled. Commit a30b85df7d599f ("kprobes: Use
> synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y") changes
> this.
Actually, if you local_irq_save(), it also disables preempt. So unless you
enables irqs, it should be safe.
Acked-by: Masami Hiramatsu <mhira...@kernel.org>
Thank you,
> Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
> ---
> arch/powerpc/kernel/optprobes.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
> index 91e037ab20a1..60ba7f1370a8 100644
> --- a/arch/powerpc/kernel/optprobes.c
> +++ b/arch/powerpc/kernel/optprobes.c
> @@ -115,7 +115,6 @@ static unsigned long can_optimize(struct kprobe *p)
> static void 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 */
> @@ -124,13 +123,14 @@ static void optimized_callback(struct optimized_kprobe
> *op,
>
> local_irq_save(flags);
> hard_irq_disable();
> + preempt_disable();
>
> if (kprobe_running()) {
> kprobes_inc_nmissed_count(&op->kp);
> } else {
> __this_cpu_write(current_kprobe, &op->kp);
> regs->nip = (unsigned long)op->kp.addr;
> - kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> + get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
> opt_pre_handler(&op->kp, regs);
> __this_cpu_write(current_kprobe, NULL);
> }
> @@ -140,6 +140,7 @@ static void optimized_callback(struct optimized_kprobe
> *op,
> * local_irq_restore() will re-enable interrupts,
> * if they were hard disabled.
> */
> + preempt_enable_no_resched();
> local_irq_restore(flags);
> }
> NOKPROBE_SYMBOL(optimized_callback);
> --
> 2.14.2
>
--
Masami Hiramatsu <mhira...@kernel.org>
