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Date:      Sat, 10 Jan 2004 15:08:22 +0100
From:      "Daan Vreeken [PA4DAN]" <Danovitsch@Vitsch.net>
To:        FreeBSD-hackers@FreeBSD.org
Subject:   kernel threads and printf locking question
Message-ID:  <200401101508.22640.Danovitsch@Vitsch.net>

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Hi,

I am writing a kernel module in which I have created a kernel thread with=
=20
kthread_create. For debugging I have added a couple of printf's in the=20
thread-routine. Running the module on a single-proc system works fine, bu=
t=20
when running it on one of my SMP machines the console freezes after a cou=
ple=20
of seconds.

I have been looking through the archives and through some other drivers (=
 for=20
example randomdev.c uses a kthread and printf's from it ). I found a vers=
ion=20
of randomdev.c with google that lock's Giant while calling printf, but=20
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=20
checks if ( curproc =3D=3D our thread ) and locks Giant if true, then pri=
ntf's.=20
(since some of the routines get called both from the thread and from othe=
r=20
places.)

What is the current state of printf-locking when called from a kernel thr=
ead?=20
Is locking Giant the only possible way to avoid problems on SMP systems, =
or=20
is there a more fine-grained printf lock available? (on 5.1-RELEASE or=20
-current)

thanks,
Daan



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