linux-kernel - Re: [PATCH v2 2/3] splice: fsnotify

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Message-ID: <CAOQ4uxiFPw-Os+Beo+F8wA1Ebc_28gTQawjob-U6PcVCwte_rg@mail.gmail.com>
Date:   Tue, 27 Jun 2023 09:27:45 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Ahelenia Ziemiańska 
        <nabijaczleweli@...ijaczleweli.xyz>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jan Kara <jack@...e.cz>,
        Chung-Chiang Cheng <cccheng@...ology.com>
Subject: Re: [PATCH v2 2/3] splice: fsnotify_modify(fd) in vmsplice

On Tue, Jun 27, 2023 at 2:09 AM Ahelenia Ziemiańska
<nabijaczleweli@...ijaczleweli.xyz> wrote:
>
> Same logic applies here: this can fill up the pipe and pollers that rely
> on getting IN_MODIFY notifications never wake up.
>
> Fixes: 983652c69199 ("splice: report related fsnotify events")
> Link: https://lore.kernel.org/linux-fsdevel/jbyihkyk5dtaohdwjyivambb2gffyjs3dodpofafnkkunxq7bu@jngkdxx65pux/t/#u
> Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@...ijaczleweli.xyz>
> ---
>  fs/splice.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/splice.c b/fs/splice.c
> index 94fae24f9d54..a18274209dc1 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -1447,6 +1447,9 @@ SYSCALL_DEFINE4(vmsplice, int, fd, const struct iovec __user *, uiov,
>         else
>                 error = vmsplice_to_user(f.file, &iter, flags);
>
> +       if (error > 0)
> +               fsnotify_modify(f.file);
> +

Wow, that is a twisted syscall, it does either write or read on the pipe
depending on whether it was open for read or write.

so you need to move fsnotify_modify() into vmsplice_to_pipe() and
add fsnotify_access() to vmsplice_to_user().

Thanks,
Amir.