linux-kernel - Re: [PATCH v3] tty: tty_io: remove hung_up_tty

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Message-ID: <b13ab60e-503a-4c11-8a99-0ccccce33c6c@I-love.SAKURA.ne.jp>
Date: Fri, 3 May 2024 01:42:12 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Marco Elver <elver@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc: paulmck@...nel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+b7c3ba8cdc2f6cf83c21@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Nathan Chancellor <nathan@...nel.org>, Arnd Bergmann <arnd@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>, Jiri Slaby <jirislaby@...nel.org>
Subject: Re: [PATCH v3] tty: tty_io: remove hung_up_tty_fops

On 2024/05/02 23:14, Marco Elver wrote:
> I sent a patch to add the type qualifier - in a simple test I added it
> does what we want:
> https://lore.kernel.org/all/20240502141242.2765090-1-elver@google.com/T/#u

Want some updates to Documentation/process/volatile-considered-harmful.rst
because __data_racy is for patches to add volatile variables ?

  Patches to remove volatile variables are generally welcome - as long as
  they come with a justification which shows that the concurrency issues have
  been properly thought through.

> 
> I'll leave it to Tetsuo to amend the original patch if __data_racy makes sense.

OK if below change is acceptable.

--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1012,7 +1012,7 @@ struct file {
        struct file_ra_state    f_ra;
        struct path             f_path;
        struct inode            *f_inode;       /* cached value */
-       const struct file_operations    *f_op;
+       const __data_racy struct file_operations   *f_op;

        u64                     f_version;
 #ifdef CONFIG_SECURITY

Hmm, debugfs assumes that f_op does not change?

fs/debugfs/file.c: In function 'full_proxy_release':
fs/debugfs/file.c:357:45: warning: initialization discards 'volatile' qualifier from pointer target type [-Wdiscarded-qualifiers]
  const struct file_operations *proxy_fops = filp->f_op;
                                             ^~~~