From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH printk v2 05/38] printk: use console_is_enabled()
Date: Mon, 31 Oct 2022 16:45:00 +0106 [thread overview]
Message-ID: <87ilk09f57.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <Y1JlerStRZ85D4Zo@alley>
On 2022-10-21, Petr Mladek <pmladek@suse.com> wrote:
>> static inline bool console_is_usable(struct console *con)
>> {
>> - if (!(con->flags & CON_ENABLED))
>> + if (!console_is_enabled(con))
>> return false;
>
> This allows to use console_is_usable() without synchronization against
> modification of the state. I guess that it will be needed for the
> printk kthreads. But it is not needed at the moment.
It will be needed once console_lock is no longer providing the
synchronization for console->flags (later in _this_ series).
I will add to the commit message that this is a preparatory change for
when console_lock no longer provides this synchronization.
>> @@ -2944,7 +2944,7 @@ void console_unblank(void)
>> console_locked = 1;
>> console_may_schedule = 0;
>> for_each_console(c)
>> - if ((c->flags & CON_ENABLED) && c->unblank)
>> + if (console_is_enabled(c) && c->unblank)
>> c->unblank();
>> console_unlock();
>
> The reading of the flag is actually synchronized against modifications
> here. I guess that we need this because c->unblank() probably is not safe
> against other operations with the console, e.g. c->write().
Again, we will need it later in this series when holding console_lock
does not provide the necessary synchronization.
>> @@ -3098,7 +3098,7 @@ static int try_enable_preferred_console(struct console *newcon,
>> * without matching. Accept the pre-enabled consoles only when match()
>> * and setup() had a chance to be called.
>> */
>> - if (newcon->flags & CON_ENABLED && c->user_specified == user_specified)
>> + if (console_is_enabled(newcon) && (c->user_specified == user_specified))
>
> This is not racy because newcon is not in console_list at this
> point. So that the state can't be modified by another callers.
>
> Anyway, it is not explicitly synchronized, so we need to use
> console_is_enabled with data_race() annotation.
For this case, it makes sense to _not_ use console_is_enabled(). This
code will be synchronized against writes even after console_lock has
been relieved of this responsibility.
Originally I wanted to replace _all_ checks with console_is_enabled(),
but since synchronization is rare, I'll keep the manual checks for those
(and add a comment that it is not a data race).
John
next prev parent reply other threads:[~2022-10-31 15:39 UTC|newest]
Thread overview: 129+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-19 14:55 [PATCH printk v2 00/38] reduce console_lock scope John Ogness
2022-10-19 14:55 ` [PATCH printk v2 01/38] serial: kgdboc: Lock console list in probe function John Ogness
2022-10-19 15:41 ` Greg Kroah-Hartman
2022-10-24 5:22 ` Sergey Senozhatsky
2022-10-25 0:34 ` Doug Anderson
2022-10-19 14:55 ` [PATCH printk v2 02/38] printk: Convert console_drivers list to hlist John Ogness
2022-10-19 15:44 ` Greg Kroah-Hartman
2022-10-19 21:46 ` John Ogness
2022-10-20 7:43 ` Greg Kroah-Hartman
2022-10-20 12:36 ` Petr Mladek
2022-10-24 5:23 ` Sergey Senozhatsky
2022-10-19 14:55 ` [PATCH printk v2 03/38] printk: Prepare for SRCU console list protection John Ogness
2022-10-19 15:16 ` Miguel Ojeda
2022-10-19 17:12 ` Paul E. McKenney
2022-10-21 8:34 ` Petr Mladek
2022-10-31 13:06 ` John Ogness
2022-10-31 14:09 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 04/38] printk: introduce console_is_enabled() wrapper John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 8:57 ` Petr Mladek
2022-10-21 9:37 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 05/38] printk: use console_is_enabled() John Ogness
2022-10-21 9:25 ` Petr Mladek
2022-10-31 15:39 ` John Ogness [this message]
2022-10-19 14:55 ` [PATCH printk v2 06/38] tty: nfcon: " John Ogness
2022-10-21 9:55 ` Petr Mladek
2022-10-31 15:59 ` John Ogness
2022-11-01 8:57 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 07/38] um: kmsg_dump: " John Ogness
2022-10-21 12:46 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 08/38] efi: earlycon: " John Ogness
2022-10-19 15:32 ` Ard Biesheuvel
2022-10-21 12:53 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 09/38] netconsole: " John Ogness
2022-10-21 13:14 ` Petr Mladek
2022-11-04 15:12 ` John Ogness
2022-10-19 14:55 ` [PATCH printk v2 10/38] tty: hvc: " John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 13:22 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 11/38] tty: serial: earlycon: " John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 13:51 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 12/38] tty: serial: kgdboc: " John Ogness
2022-10-19 16:00 ` Greg Kroah-Hartman
2022-10-21 14:10 ` Petr Mladek
2022-10-24 22:46 ` Doug Anderson
2022-10-25 0:49 ` Doug Anderson
2022-10-25 11:28 ` John Ogness
2022-11-04 16:23 ` John Ogness
2022-11-07 8:47 ` Petr Mladek
2022-11-07 9:45 ` John Ogness
2022-10-19 14:55 ` [PATCH printk v2 13/38] tty: serial: pic32_uart: " John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 14:11 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 14/38] tty: serial: samsung_tty: " John Ogness
2022-10-19 16:00 ` Greg Kroah-Hartman
2022-10-21 14:14 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 15/38] tty: serial: serial_core: " John Ogness
2022-10-19 16:00 ` Greg Kroah-Hartman
2022-10-21 14:14 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 16/38] tty: serial: xilinx_uartps: " John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 14:23 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 17/38] tty: tty_io: " John Ogness
2022-10-19 16:00 ` Greg Kroah-Hartman
2022-10-21 14:24 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 18/38] usb: early: xhci-dbc: " John Ogness
2022-10-19 16:01 ` Greg Kroah-Hartman
2022-10-21 14:27 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 19/38] kdb: kdb_io: " John Ogness
2022-10-21 14:28 ` Petr Mladek
2022-10-25 0:34 ` Doug Anderson
2022-10-19 14:55 ` [PATCH printk v2 20/38] um: kmsg_dumper: use srcu console list iterator John Ogness
2022-10-21 14:56 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 21/38] serial: kgdboc: " John Ogness
2022-10-19 16:02 ` Greg Kroah-Hartman
2022-10-21 15:09 ` Petr Mladek
2022-10-25 0:33 ` Doug Anderson
2022-10-19 14:55 ` [PATCH printk v2 22/38] serial: kgdboc: document console_lock usage John Ogness
2022-10-20 7:42 ` Greg Kroah-Hartman
2022-10-25 0:36 ` Doug Anderson
2022-10-25 10:09 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 23/38] tty: tty_io: " John Ogness
2022-10-20 7:43 ` Greg Kroah-Hartman
2022-10-25 13:31 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 24/38] xen: fbfront: use srcu console list iterator John Ogness
2022-10-25 13:39 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 25/38] proc: consoles: document console_lock usage John Ogness
2022-10-25 14:40 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 26/38] kdb: use srcu console list iterator John Ogness
2022-10-25 0:47 ` Doug Anderson
2022-10-25 14:59 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 27/38] printk: console_flush_all: " John Ogness
2022-10-25 15:17 ` Petr Mladek
2022-11-07 0:00 ` John Ogness
2022-11-07 13:03 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 28/38] printk: console_unblank: " John Ogness
2022-10-25 15:28 ` Petr Mladek
2022-10-25 15:31 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 29/38] printk: console_flush_on_panic: " John Ogness
2022-10-25 15:32 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 30/38] printk: console_device: " John Ogness
2022-10-25 15:35 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 31/38] printk: register_console: " John Ogness
2022-10-26 8:20 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 32/38] printk: __pr_flush: " John Ogness
2022-10-26 8:33 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 33/38] printk: introduce console_list_lock John Ogness
2022-10-20 7:53 ` Greg Kroah-Hartman
2022-10-27 10:09 ` Petr Mladek
2022-10-27 18:50 ` Paul E. McKenney
2022-10-28 18:09 ` Boqun Feng
2022-10-28 18:42 ` Paul E. McKenney
2022-11-07 10:10 ` John Ogness
2022-11-07 16:16 ` Paul E. McKenney
2022-10-19 14:55 ` [PATCH printk v2 34/38] serial: kgdboc: use console_list_lock instead of console_lock John Ogness
2022-10-20 7:52 ` Greg Kroah-Hartman
2022-10-27 10:13 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 35/38] tty: tty_io: use console_list_lock for list synchronization John Ogness
2022-10-20 7:43 ` Greg Kroah-Hartman
2022-10-27 10:17 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 36/38] proc: consoles: use console_list_lock for list iteration John Ogness
2022-10-27 12:02 ` Petr Mladek
2022-10-19 14:55 ` [PATCH printk v2 37/38] printk: relieve console_lock of list synchronization duties John Ogness
2022-10-27 12:40 ` Petr Mladek
2022-10-19 14:56 ` [PATCH printk v2 38/38] printk, xen: fbfront: create/use safe function for forcing preferred John Ogness
2022-10-27 13:18 ` Petr Mladek
2022-10-27 13:35 ` John Ogness
2022-10-27 14:27 ` Petr Mladek
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