Date: Sun, 11 Jan 2004 21:42:53 +0100 From: "Daan Vreeken [PA4DAN]" <Danovitsch@Vitsch.net> To: FreeBSD-current@FreeBSD.org Subject: Kernel threads and printf locking question Message-ID: <200401112142.53073.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, 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
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