From: Jiri Slaby <jirislaby@kernel.org>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Paul Cercueil <paul@crapouillou.net>,
Matthias Brugger <matthias.bgg@gmail.com>,
Andrew Jeffery <andrew@aj.id.au>,
Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
kuldip dwivedi <kuldip.dwivedi@puresoftware.com>,
Wang Qing <wangqing@vivo.com>, Andrij Abyzov <aabyzov@slb.com>,
Johan Hovold <johan@kernel.org>,
Eddie Huang <eddie.huang@mediatek.com>,
Claire Chang <tientzu@chromium.org>,
Hsin-Yi Wang <hsinyi@chromium.org>,
Zhang Qilong <zhangqilong3@huawei.com>,
"Maciej W. Rozycki" <macro@orcam.me.uk>,
Guenter Roeck <linux@roeck-us.net>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Serge Semin <Sergey.Semin@baikalelectronics.ru>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
Al Cooper <alcooperx@gmail.com>,
linux-serial@vger.kernel.org, linux-mips@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-mediatek@lists.infradead.org
Subject: Re: [PATCH printk v1 10/10] serial: 8250: implement write_atomic
Date: Thu, 5 Aug 2021 09:47:12 +0200 [thread overview]
Message-ID: <931ebc1a-3cc9-677c-44c3-7cbd645eb4f4@kernel.org> (raw)
In-Reply-To: <YQlNtr7TNAWtB8XF@smile.fi.intel.com>
On 03. 08. 21, 16:07, Andy Shevchenko wrote:
> On Tue, Aug 03, 2021 at 03:19:01PM +0206, John Ogness wrote:
>> Implement an NMI-safe write_atomic() console function in order to
>> support synchronous console printing.
>>
>> Since interrupts need to be disabled during transmit, all usage of
>> the IER register is wrapped with access functions that use the
>> printk cpulock to synchronize register access while tracking the
>> state of the interrupts. This is necessary because write_atomic()
>> can be called from an NMI context that has preempted write_atomic().
>
> ...
>
>> +static inline void serial8250_set_IER(struct uart_8250_port *up,
>> + unsigned char ier)
>> +{
>> + struct uart_port *port = &up->port;
>> + unsigned long flags;
>> + bool is_console;
>
>> + is_console = uart_console(port);
>> +
>> + if (is_console)
>> + console_atomic_cpu_lock(flags);
>> +
>> + serial_out(up, UART_IER, ier);
>> +
>> + if (is_console)
>> + console_atomic_cpu_unlock(flags);
>
> I would rewrite it as
>
> if (uart_console()) {
> console_atomic_cpu_lock(flags);
> serial_out(up, UART_IER, ier);
> console_atomic_cpu_unlock(flags);
> } else {
> serial_out(up, UART_IER, ier);
> }
>
> No additional variable, easier to get the algorithm on the first glance, less
> error prone.
Yes, the original is terrible.
Another option:
bool locked = console_atomic_cpu_lock(flags, uart_console());
serial_out(up, UART_IER, ier);
console_atomic_cpu_unlock(flags, locked);
Which makes console_atomic_cpu_lock to lock only if second parameter is
true and return its value too.
BTW I actually don't know what console_atomic_cpu_lock does to think
about it more as I was not CCed, and neither lore sees the other patches:
https://lore.kernel.org/linux-mips/20210803131301.5588-1-john.ogness@linutronix.de/
thanks,
--
js
suse labs
next prev parent reply other threads:[~2021-08-05 7:47 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-03 13:12 [PATCH printk v1 00/10] printk: introduce atomic consoles and sync mode John Ogness
2021-08-03 13:12 ` [PATCH printk v1 01/10] printk: relocate printk cpulock functions John Ogness
2021-08-04 9:24 ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 02/10] printk: rename printk cpulock API and always disable interrupts John Ogness
2021-08-04 9:52 ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 03/10] kgdb: delay roundup if holding printk cpulock John Ogness
2021-08-03 14:25 ` Daniel Thompson
2021-08-03 15:30 ` John Ogness
2021-08-04 11:31 ` Daniel Thompson
2021-08-04 12:12 ` Petr Mladek
2021-08-04 15:04 ` Daniel Thompson
2021-08-05 3:46 ` John Ogness
2021-08-06 12:06 ` Daniel Thompson
2021-08-04 12:31 ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 04/10] printk: relocate printk_delay() John Ogness
2021-08-04 13:07 ` Petr Mladek
2021-08-03 13:12 ` [PATCH printk v1 05/10] printk: call boot_delay_msec() in printk_delay() John Ogness
2021-08-04 13:09 ` Petr Mladek
2021-08-31 1:04 ` Sergey Senozhatsky
2021-08-03 13:12 ` [PATCH printk v1 06/10] printk: use seqcount_latch for console_seq John Ogness
2021-08-05 12:16 ` Petr Mladek
2021-08-05 15:26 ` John Ogness
2021-08-06 15:56 ` Petr Mladek
2021-08-31 3:05 ` Sergey Senozhatsky
2021-08-03 13:12 ` [PATCH printk v1 07/10] console: add write_atomic interface John Ogness
2021-08-03 14:02 ` Andy Shevchenko
2021-08-06 10:56 ` John Ogness
2021-08-06 11:18 ` Andy Shevchenko
2021-08-31 2:55 ` Sergey Senozhatsky
2021-08-03 13:12 ` [PATCH printk v1 08/10] printk: introduce kernel sync mode John Ogness
2021-08-05 17:11 ` Petr Mladek
2021-08-05 21:25 ` John Ogness
2021-08-03 13:13 ` [PATCH printk v1 09/10] kdb: if available, only use atomic consoles for output mirroring John Ogness
2021-08-03 13:13 ` [PATCH printk v1 10/10] serial: 8250: implement write_atomic John Ogness
2021-08-03 14:07 ` Andy Shevchenko
2021-08-05 7:47 ` Jiri Slaby [this message]
2021-08-05 8:26 ` John Ogness
2021-08-03 13:52 ` [PATCH printk v1 00/10] printk: introduce atomic consoles and sync mode Andy Shevchenko
2021-08-05 15:47 ` Petr Mladek
2021-08-31 0:33 ` Sergey Senozhatsky
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