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List:       linux-kernel
Subject:    Re: [PATCH v3] tty: tty_io: remove hung_up_tty_fops
From:       Linus Torvalds <torvalds () linux-foundation ! org>
Date:       2024-05-02 17:29:52
Message-ID: CAHk-=wi_QBG68QshO1e-xK-jt0ZFsMpZczEJe4nQMu+U7q_7EQ () mail ! gmail ! com
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On Thu, 2 May 2024 at 09:42, Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
> 
> 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;

No, this is very wrong.

It's not the *pointer* that is __data_racy. It's the structure *fied*.

So that should be

        const struct file_operations   *__data_racy f_op;

which is very different.

> 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; ^~~~

This error is a direct result of placing the __data_racy in the wrong place.

It's not that the _result_ of reading filp->f_op is racy. It's the
read of filp->f_op itself that is.

Yes, this is unusual. The *common* thing is to mark pointers as being
volatile. But this really is something entirely different from that.

               Linus


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