Kernel threads and printf locking question

Daan Vreeken [PA4DAN] Danovitsch at
Sun Jan 11 12:42:53 PST 2004


I am writing a kernel module in which I have created a kernel thread with
kthread_create. For debugging I have added a couple of printf's in the
thread routine. Running the module on a single-proc system works fine, but
when running it on one of my SMP machines the console freezes after a couple
of seconds.

I have been looking through the archives and through some other drivers ( for
example randomdev.c uses a kthread and printf's from it ). I found a version
of randomdev.c with google that lock's Giant while calling printf, but
randomdev.c in my src-tree has no locking there. (I'm using 5.1-RELEASE)
Right now I have changed all printf's in my module into a macro-function that
checks if ( curproc == our thread ) and locks Giant if true, then printf's.
(since some of the routines get called both from the thread and from other

What is the current state of printf-locking when called from a kernel thread?
Is locking Giant the only possible way to avoid problems on SMP systems, or
is there a more fine-grained printf lock available? (on 5.1-RELEASE or


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