Re: Event logging vs enhancing printk

Martin J. Bligh
2002-04-08T23:57:05Z

> I'm not aware of that being the case. The output string
> is formed into a static buffer and then copied into the
> printk ring buffer all under spinlock_irqsave(logbuf_lock).
>
> If there is something wrong then it would be occurring
> at the other end - where data is taken out of the ring
> and is sent to the console device(s). The locking there
> is OK, I think?

I think we're talking about slightly different things. I'd agree that
one call to printk is atomic, and won't get interspersed with other
things, but if we output a line via multiple calls to printk, then I
think we have a problem. Say CPU 0 executes this bit of code:

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 ?

M.