Re: [PATCHv2 perf/core 01/22] uprobes: Remove breakpoint in unapply_uprobe under mmap_write_lock

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On Thu, 15 May 2025 14:10:58 +0200
Jiri Olsa <jolsa@xxxxxxxxxx> 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 probably go away with that, 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.
> 

So, this is a bugfix, right?

Thanks,

> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>