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Date: Mon, 08 Dec 2014 13:22:14 +0000
From: "Jon Medhurst (Tixy)" <tixy@...aro.org>
To: Wang Nan <wangnan0@...wei.com>
Cc: masami.hiramatsu.pt@...achi.com, linux@....linux.org.uk,
lizefan@...wei.com, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v14 7/7] ARM: kprobes: enable OPTPROBES for ARM 32
On Mon, 2014-12-08 at 20:31 +0800, Wang Nan wrote:
> On 2014/12/8 20:06, Wang Nan wrote:
> > On 2014/12/8 19:50, Jon Medhurst (Tixy) wrote:
> >> On Mon, 2014-12-08 at 19:15 +0800, Wang Nan wrote:
> >>> On 2014/12/8 19:04, Jon Medhurst (Tixy) wrote:
> >>>> On Mon, 2014-12-08 at 14:28 +0800, Wang Nan wrote:
> [...]
> >>
> >> so another CPU could find and delete next before this one has finished
> >> doing so. Would the list end up in a consistent state where no loops
> >> develop and no probes are missed? I don't know the answer and a full
> >> analysis would be complicated, but my gut feeling is that if a cpu can
> >> observe the links in the list in an inconsistent state then only bad
> >> things can result.
> >>
> >
> > I see the problem.
> >
> > I'm thinking about making core.c and opt-arm.c to share stop_machine() code.
> > stop_machine() is required when removing breakpoint, so I'd like to define
> > a "remove_breakpoint" function in core.c and make opt-arm.c to call it.
> > Do you think it is a good idea?
> >
> >
>
> What I mean is something like this:
Yes, that should work, though as remove_breakpoint is a globally visible
symbol, I suggest a less generic name for it, perhaps
remove_kprobe_breakpoint ?
--
Tixy
> diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
> index 3a58db4..efd8ab1 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 __remove_breakpoint(void *data)
> +{
> + struct patch *p = data;
> + __patch_text(p->addr, p->insn);
> return 0;
> }
>
> +void __kprobes remove_breakpoint(void *addr, unsigned int insn)
> +{
> + struct patch p = {
> + .addr = addr,
> + .insn = insn,
> + };
> + stop_machine(__remove_breakpoint, &p, cpu_online_mask);
> +}
> +
> void __kprobes arch_disarm_kprobe(struct kprobe *p)
> {
> - stop_machine(__arch_disarm_kprobe, p, cpu_online_mask);
> + remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
> + p->opcode);
> }
>
> void __kprobes arch_remove_kprobe(struct kprobe *p)
> diff --git a/arch/arm/probes/kprobes/core.h b/arch/arm/probes/kprobes/core.h
> index f88c79f..7b7c334 100644
> --- a/arch/arm/probes/kprobes/core.h
> +++ b/arch/arm/probes/kprobes/core.h
> @@ -30,6 +30,8 @@
> #define KPROBE_THUMB16_BREAKPOINT_INSTRUCTION 0xde18
> #define KPROBE_THUMB32_BREAKPOINT_INSTRUCTION 0xf7f0a018
>
> +extern void remove_breakpoint(void *addr, unsigned int insn);
> +
> enum probes_insn __kprobes
> kprobe_decode_ldmstm(kprobe_opcode_t insn, struct arch_probes_insn *asi,
> const struct decode_header *h);
> diff --git a/arch/arm/probes/kprobes/opt-arm.c b/arch/arm/probes/kprobes/opt-arm.c
> index afbfeef..a1a1882 100644
> --- a/arch/arm/probes/kprobes/opt-arm.c
> +++ b/arch/arm/probes/kprobes/opt-arm.c
> @@ -28,8 +28,9 @@
> #include <asm/insn.h>
> /* for patch_text */
> #include <asm/patch.h>
> -/* for stop_machine */
> -#include <linux/stop_machine.h>
> +
> +#include "core.h"
> +
> /*
> * NOTE: the first sub and add instruction will be modified according
> * to the stack cost of the instruction.
> @@ -245,13 +246,8 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *or
> return 0;
> }
>
> -/*
> - * Similar to __arch_disarm_kprobe, operations which removing
> - * breakpoints must be wrapped by stop_machine to avoid racing.
> - */
> -static __kprobes int __arch_optimize_kprobes(void *p)
> +void __kprobes arch_optimize_kprobes(struct list_head *oplist)
> {
> - struct list_head *oplist = p;
> struct optimized_kprobe *op, *tmp;
>
> list_for_each_entry_safe(op, tmp, oplist, list) {
> @@ -277,16 +273,15 @@ static __kprobes int __arch_optimize_kprobes(void *p)
> op->optinsn.copied_insn[0]) & 0xf0000000) |
> (insn & 0x0fffffff);
>
> - patch_text(op->kp.addr, insn);
> + /*
> + * Similar to __arch_disarm_kprobe, operations which
> + * removing breakpoints must be wrapped by stop_machine
> + * to avoid racing.
> + */
> + remove_breakpoint(op->kp.addr, insn);
>
> list_del_init(&op->list);
> }
> - return 0;
> -}
> -
> -void arch_optimize_kprobes(struct list_head *oplist)
> -{
> - stop_machine(__arch_optimize_kprobes, oplist, cpu_online_mask);
> }
>
> void arch_unoptimize_kprobe(struct optimized_kprobe *op)
--
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