printk(9)
NAME
printk - print a kernel message
SYNOPSIS
int printk(const char * fmt, ...);
ARGUMENTS
- fmt
- format string
- ...
- variable arguments
DESCRIPTION
This is printk. It can be called from any context. We want it to work.
Be aware of the fact that if oops_in_progress is not set, we might try
to wake klogd up which could deadlock on runqueue lock if printk is
called from scheduler code.
We try to grab the console_sem. If we succeed, itīs easy - we log the
output and call the console drivers. If we fail to get the semaphore we
place the output into the log buffer and return. The current holder of
the console_sem will notice the new output in release_console_sem and
will send it to the consoles before releasing the semaphore.
One effect of this deferred printing is that code which calls printk
and then changes console_loglevel may break. This is because
console_loglevel is inspected when the actual printing occurs.