linux-kernel - Re: [PATCH 1/3] uprobes: change uprobe_register() to use uprobe_unregister() instead of __uprobe

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Message-ID: <CAEf4BzYP_WqC=+ntYw6YE83hZWi6qnPvSoTb4qt+Py-FyHcmew@mail.gmail.com>
Date: Tue, 30 Jul 2024 08:00:55 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: andrii@...nel.org, mhiramat@...nel.org, peterz@...radead.org, 
	jolsa@...nel.org, rostedt@...dmis.org, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] uprobes: change uprobe_register() to use
 uprobe_unregister() instead of __uprobe_unregister()

On Tue, Jul 30, 2024 at 5:34 AM Oleg Nesterov <oleg@...hat.com> wrote:
>
> If register_for_each_vma() fails uprobe_register() can safely drop
> uprobe->register_rwsem and use uprobe_unregister(). There is no worry
> about the races with another register/unregister, consumer_add() was
> already called so this case doesn't differ from _unregister() right
> after the successful _register().
>
> Yes this means the extra up_write() + down_write(), but this is the
> slow and unlikely case anyway.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/events/uprobes.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
>

Yep, makes total sense, in my local patches I basically already done
that as well.

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

> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 974474680820..5ea0aabe8774 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1174,16 +1174,18 @@ struct uprobe *uprobe_register(struct inode *inode,
>         if (likely(uprobe_is_active(uprobe))) {
>                 consumer_add(uprobe, uc);
>                 ret = register_for_each_vma(uprobe, uc);
> -               if (ret)
> -                       __uprobe_unregister(uprobe, uc);
>         }
>         up_write(&uprobe->register_rwsem);
>         put_uprobe(uprobe);
>
> -       if (unlikely(ret == -EAGAIN))
> -               goto retry;
> +       if (ret) {
> +               if (unlikely(ret == -EAGAIN))
> +                       goto retry;
> +               uprobe_unregister(uprobe, uc);
> +               return ERR_PTR(ret);
> +       }
>
> -       return ret ? ERR_PTR(ret) : uprobe;
> +       return uprobe;
>  }
>  EXPORT_SYMBOL_GPL(uprobe_register);
>
> --
> 2.25.1.362.g51ebf55
>