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 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 places.) 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 -current) thanks, Daan
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