linux-kernel - Re: [PATCH 2/6] uprobes/x86: Optimize is

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Message-ID: <aK1xPy33UMlT-blF@krava>
Date: Tue, 26 Aug 2025 10:33:03 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Jiri Olsa <olsajiri@...il.com>
Cc: David Laight <david.laight.linux@...il.com>,
	Peter Zijlstra <peterz@...radead.org>, oleg@...hat.com,
	andrii@...nel.org, mhiramat@...nel.org,
	linux-kernel@...r.kernel.org, alx@...nel.org, eyal.birger@...il.com,
	kees@...nel.org, bpf@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, x86@...nel.org,
	songliubraving@...com, yhs@...com, john.fastabend@...il.com,
	haoluo@...gle.com, rostedt@...dmis.org, alan.maguire@...cle.com,
	David.Laight@...lab.com, thomas@...ch.de, mingo@...nel.org,
	rick.p.edgecombe@...el.com
Subject: Re: [PATCH 2/6] uprobes/x86: Optimize is_optimize()

On Tue, Aug 26, 2025 at 10:25:29AM +0200, Jiri Olsa wrote:
> On Tue, Aug 26, 2025 at 06:51:58AM +0100, David Laight wrote:
> > On Thu, 21 Aug 2025 14:28:24 +0200
> > Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > Make is_optimized() return a tri-state and avoid return through
> > > argument. This simplifies things a little.
> > > 
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > > ---
> > >  arch/x86/kernel/uprobes.c |   34 +++++++++++++---------------------
> > >  1 file changed, 13 insertions(+), 21 deletions(-)
> > > 
> > > --- a/arch/x86/kernel/uprobes.c
> > > +++ b/arch/x86/kernel/uprobes.c
> > > @@ -1047,7 +1047,7 @@ static bool __is_optimized(uprobe_opcode
> > >  	return __in_uprobe_trampoline(vaddr + 5 + call->raddr);
> > >  }
> > >  
> > > -static int is_optimized(struct mm_struct *mm, unsigned long vaddr, bool *optimized)
> > > +static int is_optimized(struct mm_struct *mm, unsigned long vaddr)
> > >  {
> > >  	uprobe_opcode_t insn[5];
> > >  	int err;
> > > @@ -1055,8 +1055,7 @@ static int is_optimized(struct mm_struct
> > >  	err = copy_from_vaddr(mm, vaddr, &insn, 5);
> > >  	if (err)
> > >  		return err;
> > > -	*optimized = __is_optimized((uprobe_opcode_t *)&insn, vaddr);
> > > -	return 0;
> > > +	return __is_optimized((uprobe_opcode_t *)&insn, vaddr);
> > >  }
> > >  
> > >  static bool should_optimize(struct arch_uprobe *auprobe)
> > > @@ -1069,17 +1068,14 @@ int set_swbp(struct arch_uprobe *auprobe
> > >  	     unsigned long vaddr)
> > >  {
> > >  	if (should_optimize(auprobe)) {
> > > -		bool optimized = false;
> > > -		int err;
> > > -
> > >  		/*
> > >  		 * We could race with another thread that already optimized the probe,
> > >  		 * so let's not overwrite it with int3 again in this case.
> > >  		 */
> > > -		err = is_optimized(vma->vm_mm, vaddr, &optimized);
> > > -		if (err)
> > > -			return err;
> > > -		if (optimized)
> > > +		int ret = is_optimized(vma->vm_mm, vaddr);
> > > +		if (ret < 0)
> > > +			return ret;
> > > +		if (ret)
> > >  			return 0;
> > 
> > Looks like you should swap over 0 and 1.
> > That would then be: if (ret <= 0) return ret;
> 
> hum, but if it's not optimized (ret == 0) we need to follow up with
> installing breakpoint through following uprobe_write_opcode call

ah u meant to swap the whole thing.. got it

> 
> also I noticed we mix int/bool return, perhaps we could do fix below
> 
> jirka
> 
> 
> ---
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index 0a8c0a4a5423..853abb2a5638 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -1064,7 +1064,7 @@ static int is_optimized(struct mm_struct *mm, unsigned long vaddr)
>  	err = copy_from_vaddr(mm, vaddr, &insn, 5);
>  	if (err)
>  		return err;
> -	return __is_optimized((uprobe_opcode_t *)&insn, vaddr);
> +	return __is_optimized((uprobe_opcode_t *)&insn, vaddr) ? 1 : 0;
>  }
>  
>  static bool should_optimize(struct arch_uprobe *auprobe)