From: Petr Mladek <pmladek@suse.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: John Ogness <john.ogness@linutronix.de>,
linux-kernel@vger.kernel.org,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v3] printk: Skip console drivers on PREEMPT_RT.
Date: Tue, 26 Jul 2022 09:39:32 +0200 [thread overview]
Message-ID: <Yt+aNCBNk046viFq@alley> (raw)
In-Reply-To: <Yt6zwP9xSdUhsoQ9@linutronix.de>
On Mon 2022-07-25 17:16:16, Sebastian Andrzej Siewior wrote:
> printk might be invoked in a context with disabled interrupts and or
> preemption and additionally disables interrupts before it invokes the
> console drivers. This behaviour is not desired on PREEMPT_RT:
> - The console driver are using spinlock_t based locking which become sleeping
> locks on PREEMPT_RT and must not be acquired with disabled interrupts (or
> preemption).
>
> - The locks within the console drivers must remain sleeping locks and they must
> not disable interrupts. Printing (and polling for its completion) at 115200
> baud on an UART takes too long for PREEMPT_RT in general and so raises the
> latency of the IRQ-off time of the system beyond acceptable levels.
>
> Skip printing to the console as temporary workaround until the printing threads
> and atomic consoles have been introduced or another solution which is
> compatible with the PREEMPT_RT approach.
> With this change, the user will not see any kernel message printed to the
> console but can retrieve the printk buffer from userland (via the dmesg
> command). This allows enable PREEMPT_RT as a whole without disabling printk and
> loosing all kernel output.
>
> Disable console printing on PREEMPT_RT.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Thanks a lot for updating the commit message. It looks good to me now.
Reviewed-by: Petr Mladek <pmladek@suse.com>
Best Regards,
Petr
PS: John, if you ack it then I'll queue it for 5.20.
next prev parent reply other threads:[~2022-07-26 7:40 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-20 15:48 [PATCH] printk: Skip console drivers on PREEMPT_RT Sebastian Andrzej Siewior
2022-07-20 16:26 ` John Ogness
2022-07-20 16:35 ` Sebastian Andrzej Siewior
2022-07-20 17:50 ` John Ogness
2022-07-21 6:50 ` [PATCH v2] " Sebastian Andrzej Siewior
2022-07-22 12:39 ` Petr Mladek
2022-07-22 17:03 ` Sebastian Andrzej Siewior
2022-07-25 12:30 ` Petr Mladek
2022-07-25 12:51 ` John Ogness
2022-07-25 13:55 ` Sebastian Andrzej Siewior
2022-07-25 14:24 ` Petr Mladek
2022-07-25 15:16 ` [PATCH v3] " Sebastian Andrzej Siewior
2022-07-26 7:39 ` Petr Mladek [this message]
2022-07-26 7:57 ` John Ogness
2022-07-26 13:11 ` Petr Mladek
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