From: Marco Elver <elver@google.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
paulmck@kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Dmitry Vyukov <dvyukov@google.com>,
syzbot <syzbot+b7c3ba8cdc2f6cf83c21@syzkaller.appspotmail.com>,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
Nathan Chancellor <nathan@kernel.org>,
Arnd Bergmann <arnd@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Jiri Slaby <jirislaby@kernel.org>
Subject: Re: [PATCH v3] tty: tty_io: remove hung_up_tty_fops
Date: Thu, 2 May 2024 19:20:25 +0200 [thread overview]
Message-ID: <CANpmjNPtoKf1ysbKd=E8o753JT0DzBanzFBP234VBsazfufVAQ@mail.gmail.com> (raw)
In-Reply-To: <b13ab60e-503a-4c11-8a99-0ccccce33c6c@I-love.SAKURA.ne.jp>
On Thu, 2 May 2024 at 18:42, Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> 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 ?
This has nothing to do with volatile. It's merely an implementation
artifact that in CONFIG_KCSAN builds __data_racy translates to
"volatile": the compiler will emit special instrumentation for
volatile accesses so that KCSAN thinks they are "marked". However,
volatile is and has been an implementation detail of certain
primitives like READ_ONCE()/WRITE_ONCE(), although as a developer
using this interface we should not be concerned with the fact that
there's volatile underneath. In a perfect world the compiler would
give us a better "tool" than volatile, but we have to make do with the
tools we have at our disposal today.
> 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.
My suggestion is to forget about "volatile" and simply pretend it's
data_race() but as a type qualifier, like the bit of documentation I
added to Documentation/dev-tools/kcsan.rst in the patch.
> >
> > 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;
> ^~~~
Exactly as I pointed out elsewhere: pointers to __data_racy fields now
have to become __data_racy as well:
const struct file_operations __data_racy *proxy_fops = filp->f_op;
should be what you want there. The type system is in fact helping us
here as intended. :-)
next prev parent reply other threads:[~2024-05-02 17:21 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-21 8:18 [syzbot] [kernel?] KCSAN: data-race in __fput / __tty_hangup (4) syzbot
2023-04-21 8:21 ` Dmitry Vyukov
2023-04-21 15:12 ` Tetsuo Handa
2023-04-21 16:02 ` Tetsuo Handa
2023-04-23 23:34 ` Al Viro
2023-04-23 23:55 ` Tetsuo Handa
2023-04-24 0:44 ` Al Viro
2023-04-24 1:09 ` Tetsuo Handa
2023-04-25 14:47 ` Tetsuo Handa
2023-04-25 16:03 ` Al Viro
2023-04-25 22:09 ` Tetsuo Handa
2023-04-26 11:05 ` [PATCH] tty: tty_io: remove hung_up_tty_fops Tetsuo Handa
2023-04-28 16:27 ` Nathan Chancellor
2023-04-28 16:41 ` Tetsuo Handa
2023-04-28 17:11 ` Al Viro
2023-04-29 10:43 ` Tetsuo Handa
2023-04-28 17:31 ` Greg Kroah-Hartman
2023-04-29 15:21 ` Guenter Roeck
2023-05-01 18:42 ` Geert Uytterhoeven
2023-05-14 1:02 ` [PATCH v2] " Tetsuo Handa
2023-05-30 10:44 ` Greg Kroah-Hartman
2023-05-30 11:57 ` Tetsuo Handa
2023-05-30 12:51 ` Greg Kroah-Hartman
2024-04-27 6:20 ` [PATCH v3] " Tetsuo Handa
2024-04-27 19:02 ` Linus Torvalds
2024-04-28 10:19 ` Tetsuo Handa
2024-04-28 18:50 ` Linus Torvalds
2024-04-29 13:55 ` Marco Elver
2024-04-29 15:38 ` Linus Torvalds
2024-05-01 18:45 ` Paul E. McKenney
2024-05-01 18:56 ` Linus Torvalds
2024-05-01 19:02 ` Paul E. McKenney
2024-05-01 20:14 ` Marco Elver
2024-05-01 21:06 ` Linus Torvalds
2024-05-01 21:20 ` Linus Torvalds
2024-05-01 21:49 ` Paul E. McKenney
2024-05-01 22:32 ` Paul E. McKenney
2024-05-02 16:37 ` Boqun Feng
2024-05-03 23:59 ` Paul E. McKenney
2024-05-04 0:14 ` Linus Torvalds
2024-05-04 5:08 ` Paul E. McKenney
2024-05-04 17:50 ` Linus Torvalds
2024-05-04 18:18 ` Paul E. McKenney
2024-05-04 19:11 ` Linus Torvalds
2024-05-04 19:25 ` Linus Torvalds
2024-05-04 22:17 ` Paul E. McKenney
2024-05-04 22:04 ` Paul E. McKenney
2024-05-02 14:14 ` Marco Elver
2024-05-02 16:42 ` Tetsuo Handa
2024-05-02 17:20 ` Marco Elver [this message]
2024-05-02 17:29 ` Linus Torvalds
2024-05-02 18:14 ` Al Viro
2024-05-02 19:29 ` Marco Elver
2024-05-02 23:54 ` Tetsuo Handa
2024-05-03 1:12 ` Linus Torvalds
2023-04-23 13:28 ` [syzbot] [kernel?] KCSAN: data-race in __fput / __tty_hangup (4) Tetsuo Handa
2023-04-23 14:00 ` Greg Kroah-Hartman
2023-04-23 14:03 ` Greg Kroah-Hartman
2023-04-23 14:17 ` Tetsuo Handa
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