linux-kernel - Re: [PATCH 1/2] powerpc/kprobes: Remove redundant code

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Date:   Tue, 18 Feb 2020 20:09:49 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@....fr>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 1/2] powerpc/kprobes: Remove redundant code

Christophe Leroy wrote:
> At the time being we have something like
> 
> 	if (something) {
> 		p = get();
> 		if (p) {
> 			if (something_wrong)
> 				goto out;
> 			...
> 			return;
> 		} else if (a != b) {
> 			if (some_error)
> 				goto out;
> 			...
> 		}
> 		goto out;
> 	}
> 	p = get();
> 	if (!p) {
> 		if (a != b) {
> 			if (some_error)
> 				goto out;
> 			...
> 		}
> 		goto out;
> 	}
> 
> This is similar to
> 
> 	p = get();
> 	if (something) {
> 		if (p) {
> 			if (something_wrong)
> 				goto out;
> 			...
> 			return;
> 		}
> 	}
> 	if (!p) {
> 		if (a != b) {
> 			if (some_error)
> 				goto out;
> 			...
> 		}
> 		goto out;
> 	}
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
>  arch/powerpc/kernel/kprobes.c | 15 +--------------
>  1 file changed, 1 insertion(+), 14 deletions(-)

Good cleanup, thanks.

> 
> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> index f8b848aa65bd..7a925eb76ec0 100644
> --- a/arch/powerpc/kernel/kprobes.c
> +++ b/arch/powerpc/kernel/kprobes.c
> @@ -276,8 +276,8 @@ int kprobe_handler(struct pt_regs *regs)
>  	kcb = get_kprobe_ctlblk();
>  
>  	/* Check we're not actually recursing */
> +	p = get_kprobe(addr);
>  	if (kprobe_running()) {
> -		p = get_kprobe(addr);
>  		if (p) {
>  			kprobe_opcode_t insn = *p->ainsn.insn;
>  			if (kcb->kprobe_status == KPROBE_HIT_SS &&
> @@ -308,22 +308,9 @@ int kprobe_handler(struct pt_regs *regs)
>  			}
>  			prepare_singlestep(p, regs);
>  			return 1;
> -		} else if (*addr != BREAKPOINT_INSTRUCTION) {
> -			/* If trap variant, then it belongs not to us */
> -			kprobe_opcode_t cur_insn = *addr;
> -
> -			if (is_trap(cur_insn))
> -				goto no_kprobe;
> -			/* The breakpoint instruction was removed by
> -			 * another cpu right after we hit, no further
> -			 * handling of this interrupt is appropriate
> -			 */
> -			ret = 1;
>  		}
> -		goto no_kprobe;

A minot nit -- removing the above goto makes a slight change to the 
logic. But, see my comments for the next patch.

- Naveen

>  	}
>  
> -	p = get_kprobe(addr);
>  	if (!p) {
>  		if (*addr != BREAKPOINT_INSTRUCTION) {
>  			/*
> -- 
> 2.25.0
> 
>