From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Dmitry Safonov <dima@arista.com>,
linux-kernel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [RFC] printk/sysrq: Don't play with console_loglevel
Date: Wed, 29 May 2019 00:21:52 +0900 [thread overview]
Message-ID: <e0016343-2091-2478-dde3-3136a60b0942@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20190528150345.di2knfzmqfbwro3y@pathway.suse.cz>
On 2019/05/29 0:03, Petr Mladek wrote:
>> But is context dependent buffer large enough to hold SysRq-t output?
>> I think that only main logbuf can become large enough to hold SysRq-t output.
>
> SysRq messages are stored directly into the main log buffer.
>
> The limited per-CPU buffers are needed only in printk_safe
> and NMI context. We discussed it here because KERN_UNSUPPRESSED
> allows to pass the information even from this context.
>
>> We can add KERN_UNSUPPRESSED to SysRq's header line. But I don't think
>> that we can automatically add KERN_UNSUPPRESSED to SysRq's body lines
>> based on some context information. If we want to avoid manipulating
>> console_loglevel, we need to think about how to make sure that
>> KERN_UNSUPPRESSED is added to all lines from such context without
>> overflowing capacity of that buffer.
>
> We could set this context in printk_context per-CPU variable.
>
> Then we could easily add the set per-message flag in
> vprintk_store() for the normal/atomic context. And we
> could store an extra KERN_UNSUPPRESSED in printk_safe_log_store()
> for printk_safe and NMI context.
Now I got what you are trying to do. Borrow per-CPU printk_context
flags for automatically prefixing KERN_UNSUPPRESSED, based on an
assumption that any message sent during that per-CPU printk_context
flag set is important enough. Then, what we need to be careful is
nesting of setting/clearing of that flag, for NMI handler might be
called during SysRq operation is in progress. We unconditionally
prefix KERN_UNSUPPRESSED if NMI?
next prev parent reply other threads:[~2019-05-28 15:21 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-28 0:24 [RFC] printk/sysrq: Don't play with console_loglevel Dmitry Safonov
2019-05-28 3:21 ` Tetsuo Handa
2019-05-28 4:22 ` Sergey Senozhatsky
2019-05-28 8:02 ` Tetsuo Handa
2019-05-28 8:51 ` Sergey Senozhatsky
2019-05-28 10:15 ` Tetsuo Handa
2019-05-28 13:49 ` Petr Mladek
2019-06-07 17:09 ` Pavel Machek
2019-06-08 2:45 ` Tetsuo Handa
2019-06-11 15:10 ` Petr Mladek
2019-06-12 10:06 ` Tetsuo Handa
2019-05-28 4:15 ` Sergey Senozhatsky
2019-05-28 4:46 ` Sergey Senozhatsky
2019-05-28 13:42 ` Petr Mladek
2019-05-28 14:21 ` Tetsuo Handa
2019-05-28 15:03 ` Petr Mladek
2019-05-28 15:21 ` Tetsuo Handa [this message]
2019-05-28 15:58 ` Dmitry Safonov
2019-05-31 14:11 ` Tetsuo Handa
2019-06-02 6:13 ` [RFC] printk: Introduce per context console loglevel Tetsuo Handa
2019-06-06 7:59 ` Petr Mladek
2019-06-03 6:51 ` [RFC] printk/sysrq: Don't play with console_loglevel Sergey Senozhatsky
2019-06-06 7:10 ` Petr Mladek
2019-06-12 8:36 ` Sergey Senozhatsky
2019-06-12 12:00 ` Petr Mladek
2019-06-12 14:47 ` Dmitry Safonov
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