linux-kernel - Re: [PATCHv3 perf/core 07/22] uprobes: Add do_ref_ctr argument to uprobe

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Message-Id: <20250625154259.4a092f0213739404a0e9b210@kernel.org>
Date: Wed, 25 Jun 2025 15:42:59 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 x86@...nel.org, Song Liu <songliubraving@...com>, Yonghong Song
 <yhs@...com>, John Fastabend <john.fastabend@...il.com>, Hao Luo
 <haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Alan Maguire <alan.maguire@...cle.com>, David Laight
 <David.Laight@...LAB.COM>, Thomas Weißschuh
 <thomas@...ch.de>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCHv3 perf/core 07/22] uprobes: Add do_ref_ctr argument to
 uprobe_write function

On Thu,  5 Jun 2025 15:23:34 +0200
Jiri Olsa <jolsa@...nel.org> wrote:

> Making update_ref_ctr call in uprobe_write conditional based
> on do_ref_ctr argument. This way we can use uprobe_write for
> instruction update without doing ref_ctr_offset update.
> 

Can we just decouple this update from uprobe_write()?
If we do this exclusively, I think we can do something like;

lock()
update_ref_ctr(uprobe, mm, +1);
...
ret = uprobe_write();
...
if (ret < 0)
  update_ref_ctr(uprobe, mm, -1);
unlock()

Thank you,


> Acked-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  include/linux/uprobes.h | 2 +-
>  kernel/events/uprobes.c | 8 ++++----
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 518b26756469..5080619560d4 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -200,7 +200,7 @@ extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
>  extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma, unsigned long vaddr, uprobe_opcode_t,
>  			       bool is_register);
>  extern int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma, const unsigned long opcode_vaddr,
> -			uprobe_opcode_t *insn, int nbytes, uprobe_write_verify_t verify, bool is_register);
> +			uprobe_opcode_t *insn, int nbytes, uprobe_write_verify_t verify, bool is_register, bool do_update_ref_ctr);
>  extern struct uprobe *uprobe_register(struct inode *inode, loff_t offset, loff_t ref_ctr_offset, struct uprobe_consumer *uc);
>  extern int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool);
>  extern void uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc);
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 1e5dc3b30707..6795b8d82b9c 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -492,12 +492,12 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  		bool is_register)
>  {
>  	return uprobe_write(auprobe, vma, opcode_vaddr, &opcode, UPROBE_SWBP_INSN_SIZE,
> -			    verify_opcode, is_register);
> +			    verify_opcode, is_register, true /* do_update_ref_ctr */);
>  }
>  
>  int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  		 const unsigned long insn_vaddr, uprobe_opcode_t *insn, int nbytes,
> -		 uprobe_write_verify_t verify, bool is_register)
> +		 uprobe_write_verify_t verify, bool is_register, bool do_update_ref_ctr)
>  {
>  	const unsigned long vaddr = insn_vaddr & PAGE_MASK;
>  	struct mm_struct *mm = vma->vm_mm;
> @@ -538,7 +538,7 @@ int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  	}
>  
>  	/* We are going to replace instruction, update ref_ctr. */
> -	if (!ref_ctr_updated && uprobe->ref_ctr_offset) {
> +	if (do_update_ref_ctr && !ref_ctr_updated && uprobe->ref_ctr_offset) {
>  		ret = update_ref_ctr(uprobe, mm, is_register ? 1 : -1);
>  		if (ret) {
>  			folio_put(folio);
> @@ -590,7 +590,7 @@ int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
>  
>  out:
>  	/* Revert back reference counter if instruction update failed. */
> -	if (ret < 0 && ref_ctr_updated)
> +	if (do_update_ref_ctr && ret < 0 && ref_ctr_updated)
>  		update_ref_ctr(uprobe, mm, is_register ? -1 : 1);
>  
>  	/* try collapse pmd for compound page */
> -- 
> 2.49.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>