Messages in this thread | | | Date | Tue, 09 Dec 2014 19:25:06 +0900 | From | Masami Hiramatsu <> | Subject | Re: Re: [RESEND][PATCH v15 7/7] ARM: kprobes: enable OPTPROBES for ARM 32 |
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(2014/12/09 18:14), Jon Medhurst (Tixy) wrote: [...] >>> diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c >>> index 3a58db4..a4ec240 100644 >>> --- a/arch/arm/probes/kprobes/core.c >>> +++ b/arch/arm/probes/kprobes/core.c >>> @@ -163,19 +163,31 @@ void __kprobes arch_arm_kprobe(struct kprobe *p) >>> * memory. It is also needed to atomically set the two half-words of a 32-bit >>> * Thumb breakpoint. >>> */ >>> -int __kprobes __arch_disarm_kprobe(void *p) >>> -{ >>> - struct kprobe *kp = p; >>> - void *addr = (void *)((uintptr_t)kp->addr & ~1); >>> - >>> - __patch_text(addr, kp->opcode); >>> +struct patch { >>> + void *addr; >>> + unsigned int insn; >>> +}; >>> >>> +static int __kprobes_remove_breakpoint(void *data) >>> +{ >>> + struct patch *p = data; >>> + __patch_text(p->addr, p->insn); >>> return 0; >>> } >>> >>> +void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn) >>> +{ >>> + struct patch p = { >>> + .addr = addr, >>> + .insn = insn, >>> + }; >>> + stop_machine(__kprobes_remove_breakpoint, &p, cpu_online_mask); >>> +} >> >> Hmm, I think finally we should fix patch_text() in patch.c to forcibly use stop_machine >> by adding "bool stop" parameter, instead of introducing new another patch_text() >> implementation, because we'd better avoid two private "patch" data structures. > > That was my first thought too, then I realised that breaks encapsulation > of the patch_text implementation, because its use of stop_machine is an > implementation detail and it could be rewritten to not use stop machine. > (That is sort of on my long term todo list > https://lkml.org/lkml/2014/9/4/188)
Indeed. OK, now let it goes. :)
> Whereas stop machine is used by kprobes to avoid race conditions with > the undefined instruction exception handler and something like that > would be needed even if patch_text didn't use stop_machine.
At this point, it's OK.
However, I'm not convinced completely. Perhaps, it depends on cache-coherent bus implementation, but there may be some implementations which can allow us to change one instruction atomically without stop_machine.
I'm actually interested in PREEMPT_RT on arm32, and this stop_machine() is a barrier to apply kprobes on real-time systems.
Thank you,
-- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com
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