Sorry for the late reply. Coming back from Kernel Recipes, I fell way behind in email.
On Fri, 29 Sep 2017 00:29:38 -0700 Masami Hiramatsu <mhira...@kernel.org> wrote: > > > + * are done. Because optprobe may modify multiple instructions, > > > + * there is a chance that the Nth instruction is interrupted. In that > > > + * case, running interrupt can return to the Nth byte of jump > > > + * instruction. This can be avoided by waiting for returning of > > > + * such interrupts, since (until here) the first byte of the optimized > > > + * probe is already replaced with normal kprobe (sw breakpoint) and > > > + * all threads which reach to the probed address will hit it and > > > + * bypass the copied instructions (instead of executing the original.) > > > + * With CONFIG_PREEMPT, such interrupts can be preepmted. To wait > > > + * for such thread, we will use synchronize_rcu_tasks() which ensures > > > + * all preeempted tasks are scheduled normally (not preempted). > > > + * So we can ensure there is no threads preempted at probed address. > > > > What? Interrupts cannot be preempted. > > Steve, could you correct me if I'm wrong. I thought if the kernel is > compiled with CONFIG_PREEMPT=y, even in the kernel, it can be preempted > suddenly. It means timer interrupt occurs at kernel path and it yield > to new task (=preempt.) Do I miss something? The above sounds correct. I believe Ingo was pointing out the line that states "With CONFIG_PREEMPT, such interrupts can be preempted", which is not true. I think you meant that interrupts can preempt the kernel and cause it to schedule out. The line above sounds like you meant the interrupt was preempted, which can't happen. -- Steve
