On (09/28/18 20:01), Tetsuo Handa wrote:
> > Yes, this makes sense. At the same time we can keep pr_line buffer
> > in .bss
> >
> > static char buffer[1024];
> > static DEFINE_PR_LINE_BUF(..., buffer);
> >
> > just like you have already mentioned. But that's going to require a
> > case-by-case handling; so a big list of printk buffers is a simpler
> > option. Fallback, tho, can be painful. On a system with 1024 CPUs can
> > one have more than 16 concurrent cont printks? If the answer is yes,
> > then we are looking at the same broken cont output as before.
>
> I'm OK with making "16" configurable (at kernel configuration and/or
> at kernel boot like log_buf_len= kernel command line parameter).
Do we really want this? Why .bss placement doesn't work for you?
void oom(...)
{
static DEFINE_PR_LINE(KERN_ERR, pr);
pr_line(&pr, ....);
pr_line(&pr, "\n");
}
the underlying buffer will be static; the pr_line will get re-init
(offset = 0) every time we call the function, which is OK. And we can
pass &pr to any function oom() invokes. What am I missing?
> We could even allow each "struct task_struct" to have corresponding
> "struct printk_buffer".
Tetsuo, realistically, we can't. Sorry. No one will let us to have a printk
buffer on per-task_struct basis. Even if someone will let us to do this,
a miracle, a single per-task_struct buffer won't work. Because, then
someone will discover that a very simple API
buffered_printk(current->printk_buffer, "......");
does not work if buffered_printk() gets interrupted by IRQ, etc. in case
if that new context also does
buffered_printk(current->printk_buffer, "......");
So then we will have per-context per-task_struct printk buffer: for task,
for exceptions, for softirq, for hardirq, for NMI, etc. This is not worth
it.
Let's just have a very simple seq_buf based pr_line API. No config options,
no command line arguments - heap, bss or stack for buffer placement. Or even
simpler.
-ss
