linux-kernel - Re: [PATCH perf/core 07/22] uprobes: Remove breakpoint in unapply_uprobe under mmap_write

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Message-ID: <CAEf4BzbtUMCCY8FPjRjc8i5newEoKkz7S-j-LOpD6TJzOogNtg@mail.gmail.com>
Date: Tue, 22 Apr 2025 16:48:24 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
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: [PATCH perf/core 07/22] uprobes: Remove breakpoint in
 unapply_uprobe under mmap_write_lock

On Mon, Apr 21, 2025 at 2:45 PM 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 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.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  kernel/events/uprobes.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>

Makes sense.

Acked-by: Andrii Nakryiko <andrii@...nel.org>


> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index c8d88060dfbf..d256c695d7ff 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1483,7 +1483,7 @@ 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;
> @@ -1500,7 +1500,7 @@ 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
>