Re: [PATCH v6 1/3] printk: Add line-buffered printk() API.

[Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>]

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.