Re: possible circular locking dependency detected [was: linux-next: Tree for Aug 22]

Sergey Senozhatsky
2017-08-23T05:44:38Z

On (08/23/17 13:35), Boqun Feng wrote:
[..]
> > > printk(KERN_CONT ");\n");
> >
> > KERN_CONT and "\n" should not be together. "\n" flushes the cont
> > buffer immediately.
> >
>
> Hmm.. Not quite familiar with printk() stuffs, but I could see several
> usages of printk(KERN_CONT "...\n") in kernel.
>
> Did a bit research myself, and I now think the inappropriate use is to
> use a KERN_CONT printk *after* another printk ending with a "\n". Am I
> missing some recent changes or rules of KERN_CONT?

has been this way for quite some time (if not always).

LOG_NEWLINE results in cont_flush(), which log_store() the content
of KERN_CONT buffer.

if we see that supplied message has no \n then we store it in a
dedicated buffer (cont buffer)

if (!(lflags & LOG_NEWLINE))
return cont_add();

return log_store();

we flush that buffer (move its content to the kernel log buffer) when
we receive a message with a \n or when printk() from another task/context
interrupts the current cont line and, thus, forces us to flush.

-ss