Re: Event logging vs enhancing printk

Andrew Morton
2002-04-09T00:09:22Z

"Martin J. Bligh" wrote:
>
> ...
> for (i=0; i<10; i++) { printk ("%d ", i); } printk("\n");
>
> and CPU 1 does "printk("hello\n");" then instead of getting either
>
> 0 1 2 3 4 5 6 7 8 9
> hello
>
> or
>
> hello
> 0 1 2 3 4 5 6 7 8 9
>
> either of which would be fine, we may get
>
> 0 1 2 3 hello
> 4 5 6 7 8 9
>
> which I don't think is fine - obviously the example is somewhat
> trite, but with the real instances of things that build output for one
> line through multiple calls to printk, you can get unreadable garbage,
> if I read the code correctly ?

Ah. Yes, that will definitely happen. We only have atomicity
at the level of a single printk call.

It would be feasible to introduce additional locking so that
multiple printks can be made atomic. This should be resisted
though - printk needs to be really robust, and needs to have
a good chance of working even when the machine is having hysterics.
It's already rather complex.

For the rare cases which you cite we can use a local staging
buffer and sprintf, or just live with it, I suspect.

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