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Message-ID: <c1f9b048-e4ed-bc69-9ee6-6fe24233de4a@i-love.sakura.ne.jp>
Date: Thu, 8 Nov 2018 20:46:28 +0900
From: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To: Petr Mladek <pmladek@...e.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Dmitriy Vyukov <dvyukov@...gle.com>,
Steven Rostedt <rostedt@...dmis.org>,
Alexander Potapenko <glider@...gle.com>,
Fengguang Wu <fengguang.wu@...el.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v6 1/3] printk: Add line-buffered printk() API.
On 2018/11/08 20:24, Petr Mladek wrote:
>> Let's have one more look at what we will fix and what we will break.
>>
>> 'cont' has premature flushes.
>>
>> Why is it good.
>> It preserves the correct order of events.
>>
>> pr_cont("calling foo->init()....");
>> foo->init()
>> printk("Can't allocate buffer\n"); // premature flush
>> pr_cont("...blah\h");
>>
>> Will end up in the logbuf as:
>> [12345.123] calling foo->init()....
>> [12345.124] Can't allocate buffer
>> [12345.125] ...blah
>>
>> Where buffered printk will endup as:
>> [12345.123] Can't allocate buffer
>> [12345.124] calling foo->init().......blah
>
> We will always have this problem with API using explicit buffers.
> What do you suggest instead, please?
>
> I am afraid that we are running in cycles. The other serious
> alternative was having per-process and per-context buffers
> but it was rejected several times.
Is it possible to identify all locations which should use their own
printk() buffers (e.g. interrupt handlers, oops handlers) ? If yes,
automatically switching printk() buffers (like memalloc_nofs_save()/
memalloc_nofs_restore()) will be easiest and least error prone.
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