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From: "Daan Vreeken [PA4DAN]" <Danovitsch@Vitsch.net>
Date: Sun, 11 Jan 2004 21:42:53 +0100
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Subject: Kernel threads and printf locking question
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Hi,

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, bu=
t
when running it on one of my SMP machines the console freezes after a cou=
ple
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 vers=
ion
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 =3D=3D our thread ) and locks Giant if true, then pri=
ntf's.
(since some of the routines get called both from the thread and from othe=
r
places.)

What is the current state of printf-locking when called from a kernel thr=
ead?
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
-current)

thanks,
Daan