linux-kernel - Re: [PATCHv3 perf/core 01/22] uprobes: Remove breakpoint in unapply_uprobe under mmap_write

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Message-Id: <20250625150429.0623e05b3b1bba2d95b57dc5@kernel.org>
Date: Wed, 25 Jun 2025 15:04:29 +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 01/22] uprobes: Remove breakpoint in
 unapply_uprobe under mmap_write_lock

On Thu,  5 Jun 2025 15:23:28 +0200
Jiri Olsa <jolsa@...nel.org> wrote:

> Currently unapply_uprobe takes mmap_read_lock, but it might call
> remove_breakpoint which eventually changes user pages.
> 
> Current code writes either breakpoint or original instruction, so it can
> go away with read lock as explained in here [1]. But with the upcoming
> change that writes multiple instructions on the probed address we need
> to ensure that any update to mm's pages is exclusive.
> 
> [1] https://lore.kernel.org/all/20240710140045.GA1084@redhat.com/
> 

Looks good to me.

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

Thanks,



> Acked-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  kernel/events/uprobes.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 84ee7b590861..257581432cd8 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -483,7 +483,7 @@ static int __uprobe_write_opcode(struct vm_area_struct *vma,
>   * @opcode_vaddr: the virtual address to store the opcode.
>   * @opcode: opcode to be written at @opcode_vaddr.
>   *
> - * Called with mm->mmap_lock held for read or write.
> + * Called with mm->mmap_lock held for write.
>   * Return 0 (success) or a negative errno.
>   */
>  int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> @@ -1464,7 +1464,7 @@ static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)
>  	struct vm_area_struct *vma;
>  	int err = 0;
>  
> -	mmap_read_lock(mm);
> +	mmap_write_lock(mm);
>  	for_each_vma(vmi, vma) {
>  		unsigned long vaddr;
>  		loff_t offset;
> @@ -1481,7 +1481,7 @@ static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)
>  		vaddr = offset_to_vaddr(vma, uprobe->offset);
>  		err |= remove_breakpoint(uprobe, vma, vaddr);
>  	}
> -	mmap_read_unlock(mm);
> +	mmap_write_unlock(mm);
>  
>  	return err;
>  }
> -- 
> 2.49.0
> 


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