From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Daniel Wang <wonderfly@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
Jiri Slaby <jslaby@suse.com>, Peter Feiner <pfeiner@google.com>,
linux-serial@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [RFC PATCH v1 15/25] printk: print history for new consoles
Date: Tue, 26 Feb 2019 16:22:01 +0100 [thread overview]
Message-ID: <87o96yziau.fsf@linutronix.de> (raw)
In-Reply-To: <20190226145837.wl54fr7rn2ii5oxc@pathway.suse.cz> (Petr Mladek's message of "Tue, 26 Feb 2019 15:58:37 +0100")
On 2019-02-26, Petr Mladek <pmladek@suse.com> wrote:
>> When new consoles register, they currently print how many messages
>> they have missed. However, many (or all) of those messages may still
>> be in the ring buffer. Add functionality to print as much of the
>> history as available. This is a clean replacement of the old
>> exclusive console hack.
>>
>> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
>> index 897219f34cab..6c875abd7b17 100644
>> --- a/kernel/printk/printk.c
>> +++ b/kernel/printk/printk.c
>> @@ -1506,6 +1506,77 @@ static void format_text(struct printk_log *msg, u64 seq,
>> }
>> }
>>
>> +static void printk_write_history(struct console *con, u64 master_seq)
>> +{
>> + struct prb_iterator iter;
>> + bool time = printk_time;
>> + static char *ext_text;
>> + static char *text;
>> + static char *buf;
>> + u64 seq;
>> +
>> + ext_text = kmalloc(CONSOLE_EXT_LOG_MAX, GFP_KERNEL);
>> + text = kmalloc(PRINTK_SPRINT_MAX, GFP_KERNEL);
>> + buf = kmalloc(PRINTK_RECORD_MAX, GFP_KERNEL);
>> + if (!ext_text || !text || !buf)
>> + return;
>
> We need to free buffers that were successfully allocated.
Ouch. You just found some crazy garbage. The char-pointers are
static. The bug is that it allocates each time a console is
registered. It was supposed to be lazy allocation:
if (!ext_text)
ext_text = kmalloc(CONSOLE_EXT_LOG_MAX, GFP_KERNEL);
>> + if (!(con->flags & CON_ENABLED))
>> + goto out;
>> +
>> + if (!con->write)
>> + goto out;
>> +
>> + if (!cpu_online(raw_smp_processor_id()) &&
>> + !(con->flags & CON_ANYTIME))
>> + goto out;
>> +
>> + prb_iter_init(&iter, &printk_rb, NULL);
>> +
>> + for (;;) {
>> + struct printk_log *msg;
>> + size_t ext_len;
>> + size_t len;
>> + int ret;
>> +
>> + ret = prb_iter_next(&iter, buf, PRINTK_RECORD_MAX, &seq);
>> + if (ret == 0) {
>> + break;
>> + } else if (ret < 0) {
>> + prb_iter_init(&iter, &printk_rb, NULL);
>> + continue;
>> + }
>> +
>> + if (seq > master_seq)
>> + break;
>> +
>> + con->printk_seq++;
>> + if (con->printk_seq < seq) {
>> + print_console_dropped(con, seq - con->printk_seq);
>> + con->printk_seq = seq;
>> + }
>> +
>> + msg = (struct printk_log *)buf;
>> + format_text(msg, master_seq, ext_text, &ext_len, text,
>> + &len, time);
>> +
>> + if (len == 0 && ext_len == 0)
>> + continue;
>> +
>> + if (con->flags & CON_EXTENDED)
>> + con->write(con, ext_text, ext_len);
>> + else
>> + con->write(con, text, len);
>> +
>> + printk_delay(msg->level);
>
> Hmm, this duplicates a lot of code from call_console_drivers() and
> maybe also from printk_kthread_func(). It is error prone. People
> will forget to update this function when working on the main one.
>
> We need to put the shared parts into separate functions.
Agreed.
>> + }
>> +out:
>> + con->wrote_history = 1;
>> + kfree(ext_text);
>> + kfree(text);
>> + kfree(buf);
>> +}
>> +
>> /*
>> * Call the console drivers, asking them to write out
>> * log_buf[start] to log_buf[end - 1].
>> @@ -1524,6 +1595,10 @@ static void call_console_drivers(u64 seq, const char *ext_text, size_t ext_len,
>> for_each_console(con) {
>> if (!(con->flags & CON_ENABLED))
>> continue;
>> + if (!con->wrote_history) {
>> + printk_write_history(con, seq);
>
> This looks like an alien. The code is supposed to write one message
> from the given buffer. And some huge job is well hidden there.
This is a very simple implementation of a printk kthread. It probably
makes more sense to have a printk kthread per console. That would allow
fast consoles to not be penalized by slow consoles. Due to the
per-console seq tracking, the code would already support it.
> In addition, the code is actually recursive. It will become
> clear when it is deduplicated as suggested above. We should
> avoid it when it is not necessary. Note that recursive code
> is always more prone to mistakes and it is harder to think of.
Agreed.
> I guess that the motivation is to do everything from the printk
> kthread. Is it really necessary? register_console() takes
> console_lock(). It has to be sleepable context by definition.
It is not necessary. It is desired. Why should _any_ task be punished
with console writing? That is what the printk kthread is for.
John Ogness
next prev parent reply other threads:[~2019-02-26 15:22 UTC|newest]
Thread overview: 147+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-12 14:29 [RFC PATCH v1 00/25] printk: new implementation John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 01/25] printk-rb: add printk ring buffer documentation John Ogness
2019-02-12 14:45 ` Greg Kroah-Hartman
2019-02-12 14:29 ` [RFC PATCH v1 02/25] printk-rb: add prb locking functions John Ogness
2019-02-13 15:45 ` Petr Mladek
2019-02-13 21:39 ` John Ogness
2019-02-14 10:33 ` Petr Mladek
2019-02-14 12:10 ` John Ogness
2019-02-15 10:26 ` Petr Mladek
2019-02-15 10:56 ` John Ogness
2019-03-07 2:12 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 03/25] printk-rb: define ring buffer struct and initializer John Ogness
2019-02-12 14:46 ` Greg Kroah-Hartman
2019-02-14 12:46 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 04/25] printk-rb: add writer interface John Ogness
2019-02-14 15:16 ` Petr Mladek
2019-02-14 23:36 ` John Ogness
2019-02-15 1:19 ` John Ogness
2019-02-15 13:47 ` Petr Mladek
2019-02-17 1:32 ` John Ogness
2019-02-21 13:51 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 05/25] printk-rb: add basic non-blocking reading interface John Ogness
2019-02-18 12:54 ` Petr Mladek
2019-02-19 21:44 ` John Ogness
2019-02-21 16:22 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 06/25] printk-rb: add blocking reader support John Ogness
2019-02-18 14:05 ` Petr Mladek
2019-02-19 21:47 ` John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 07/25] printk-rb: add functionality required by printk John Ogness
2019-02-12 17:15 ` Linus Torvalds
2019-02-13 9:20 ` John Ogness
2019-02-18 15:59 ` Petr Mladek
2019-02-19 22:08 ` John Ogness
2019-02-22 9:58 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 08/25] printk: add ring buffer and kthread John Ogness
2019-02-12 15:47 ` Sergey Senozhatsky
2019-02-19 13:54 ` Petr Mladek
2019-03-04 7:38 ` Sergey Senozhatsky
2019-03-04 10:00 ` Sergey Senozhatsky
2019-03-04 11:07 ` Sergey Senozhatsky
2019-03-05 21:00 ` John Ogness
2019-03-06 15:57 ` Petr Mladek
2019-03-06 21:17 ` John Ogness
2019-03-06 22:22 ` John Ogness
2019-03-07 6:41 ` Sergey Senozhatsky
2019-03-07 6:51 ` Sergey Senozhatsky
2019-03-07 12:50 ` Petr Mladek
2019-03-07 5:15 ` Sergey Senozhatsky
2019-03-11 10:51 ` John Ogness
2019-03-12 9:58 ` Sergey Senozhatsky
2019-03-12 10:30 ` Petr Mladek
2019-03-07 12:06 ` John Ogness
2019-03-08 1:31 ` Sergey Senozhatsky
2019-03-08 10:04 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 09/25] printk: remove exclusive console hack John Ogness
2019-02-19 14:03 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 10/25] printk: redirect emit/store to new ringbuffer John Ogness
2019-02-20 9:01 ` Petr Mladek
2019-02-20 21:25 ` John Ogness
2019-02-22 14:43 ` Petr Mladek
2019-02-22 15:06 ` John Ogness
2019-02-22 15:25 ` Petr Mladek
2019-02-25 12:11 ` Petr Mladek
2019-02-25 16:41 ` John Ogness
2019-02-26 9:45 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 11/25] printk_safe: remove printk safe code John Ogness
2019-02-22 10:37 ` Petr Mladek
2019-02-22 13:38 ` John Ogness
2019-02-22 15:15 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 12/25] printk: minimize console locking implementation John Ogness
2019-02-25 13:44 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 13/25] printk: track seq per console John Ogness
2019-02-25 14:59 ` Petr Mladek
2019-02-26 8:45 ` John Ogness
2019-02-26 13:11 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 14/25] printk: do boot_delay_msec inside printk_delay John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 15/25] printk: print history for new consoles John Ogness
2019-02-26 14:58 ` Petr Mladek
2019-02-26 15:22 ` John Ogness [this message]
2019-02-27 9:02 ` Petr Mladek
2019-02-27 10:02 ` John Ogness
2019-02-27 13:12 ` Petr Mladek
2019-03-04 9:24 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 16/25] printk: implement CON_PRINTBUFFER John Ogness
2019-02-26 15:38 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 17/25] printk: add processor number to output John Ogness
2019-02-13 22:29 ` John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 18/25] console: add write_atomic interface John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 19/25] printk: introduce emergency messages John Ogness
2019-03-07 7:30 ` Sergey Senozhatsky
2019-03-08 10:31 ` Petr Mladek
2019-03-11 12:04 ` John Ogness
2019-03-12 2:51 ` Sergey Senozhatsky
2019-03-12 2:58 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 20/25] serial: 8250: implement write_atomic John Ogness
2019-02-27 9:46 ` Petr Mladek
2019-02-27 10:32 ` John Ogness
2019-02-27 13:55 ` Petr Mladek
2019-03-08 4:05 ` John Ogness
2019-03-08 4:17 ` John Ogness
2019-03-08 10:28 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 21/25] printk: implement KERN_CONT John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 22/25] printk: implement /dev/kmsg John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 23/25] printk: implement syslog John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 24/25] printk: implement kmsg_dump John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 25/25] printk: remove unused code John Ogness
2019-03-08 14:02 ` Sebastian Andrzej Siewior
2019-03-11 2:46 ` Sergey Senozhatsky
2019-03-11 8:18 ` Sebastian Andrzej Siewior
2019-03-12 9:38 ` Petr Mladek
2019-02-13 1:31 ` [RFC PATCH v1 00/25] printk: new implementation Sergey Senozhatsky
2019-02-13 13:43 ` John Ogness
2019-03-04 6:39 ` Sergey Senozhatsky
2019-02-13 1:41 ` Sergey Senozhatsky
2019-02-13 14:15 ` John Ogness
2019-03-04 5:31 ` Sergey Senozhatsky
2019-02-13 2:55 ` Sergey Senozhatsky
2019-02-13 14:43 ` John Ogness
2019-03-04 5:23 ` Sergey Senozhatsky
2019-03-07 9:53 ` John Ogness
2019-03-08 10:00 ` Petr Mladek
2019-03-11 10:54 ` Sergey Senozhatsky
2019-03-12 12:38 ` Petr Mladek
2019-03-12 15:15 ` John Ogness
2019-03-13 2:15 ` Sergey Senozhatsky
2019-03-13 8:19 ` John Ogness
2019-03-13 8:40 ` Sebastian Siewior
2019-03-13 9:27 ` Sergey Senozhatsky
2019-03-13 10:06 ` Sergey Senozhatsky
2019-03-14 9:27 ` Petr Mladek
2019-03-13 8:46 ` Sergey Senozhatsky
2019-03-14 9:14 ` Petr Mladek
2019-03-14 9:35 ` John Ogness
2019-03-13 2:00 ` Sergey Senozhatsky
2019-02-13 16:54 ` David Laight
2019-02-13 22:20 ` John Ogness
2020-01-20 23:05 ` Eugeniu Rosca
2020-01-21 23:56 ` John Ogness
2020-01-22 2:34 ` Eugeniu Rosca
2020-01-22 7:31 ` Geert Uytterhoeven
2020-01-22 16:58 ` Eugeniu Rosca
2020-01-22 19:48 ` Geert Uytterhoeven
2020-01-24 16:09 ` Eugeniu Rosca
2020-01-27 12:32 ` Petr Mladek
2020-01-27 13:45 ` Eugeniu Rosca
2020-01-22 10:33 ` John Ogness
2020-01-24 12:13 ` Eugeniu Rosca
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