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SubjectRe: printk loglevel policy?
Jim Nelson wrote:
> Alan Cox wrote:
>> On Gwe, 2004-12-31 at 02:20, Coywolf Qi Hunt wrote:
>>> Hi all,
>>> Recently, I've seen a lot of add loglevel to printk patches. grep
>>> 'printk("' -r | wc shows me 2433. There are probably 2433 printk
>>> need to patch, is it? What's this printk loglevel policy, all these
>> You would need to work out which were at the start of a newline - most
>> of them are probably just fine and valid
> That reminds me of a question I've had inthe back of my head. When you
> have a SMP system wouldn't it be possible to have:
> CPU 1 (running func1) CPU 2 (running func2)
> | |
> printk ("foo..."); |
> | printk ("bleh\n");
> printk ("finished\n); |
> printk ("readout from bleh\n";
> Is that possible? Especially if the process on CPU 1 slept on a
> semaphore or something similar?
> Or does printk() do some tracking that I didn't see as to where in the
> kernel the strings are coming from?

That kind of garbled output has been known to happen, but
the <console_sem> is supposed to prevent that (along with
zap_locks() in kernel/printk.c).

If it still happens, it needs to be fixed.
David Howells (RH) has posted patches that fix it.

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