Re: [PATCH perf/core 07/22] uprobes: Remove breakpoint in unapply_uprobe under mmap_write_lock

Andrii Nakryiko
2025-04-22T23:49:02Z

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

Makes sense.

Acked-by: Andrii Nakryiko <andrii@kernel.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
>