BUG_ON() in ksoftirqd is a bit too agressive...

PATCH In review George Anzinger 2 participants 2 messages May 18, 2005 – May 23, 2005

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George Anzinger

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2005-05-18 23:52 UTC #0 lore raw

PATCH 1/1 BUG_ON() in ksoftirqd is a bit too agressive...

Ksoftirqd is created by init, long after the timer system is up and running. We have hit the BUG_ON(tasklet_... in this code, i.e. tasklets pending at ksoftirqd create time. Since, with the RT option to push all softirq code to a thread, any softirqs are defered to this time, it is easy to hit this bug. Clearly only a problem for cpu 0. Here is a patch:

kernel/softirq.c +6 -2

Index: linux-2.6.10/kernel/softirq.c
===================================================================
@@ -514,8 +514,12 @@
 
 	switch (action) {
 	case CPU_UP_PREPARE:
-		BUG_ON(per_cpu(tasklet_vec, hotcpu).list);
-		BUG_ON(per_cpu(tasklet_hi_vec, hotcpu).list);
+		/* We may have tasklets already scheduled on
+		   processor 0, so don't check there. */
+		if (hotcpu != 0) {
+			BUG_ON(per_cpu(tasklet_vec, hotcpu).list);
+			BUG_ON(per_cpu(tasklet_hi_vec, hotcpu).list);
+		}
 		p = kthread_create(ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
 		if (IS_ERR(p)) {
 			printk("ksoftirqd for %i failed\n", hotcpu);

Signature · 2 lines

George Anzinger   [email protected]
High-res-timers:  http://sourceforge.net/projects/high-res-timers/

Ingo Molnar

2005-05-23 07:29 UTC #1 lore raw

Quoted 6 lines · George Anzinger

Ksoftirqd is created by init, long after the timer system is up and running. We have hit the BUG_ON(tasklet_... in this code, i.e. tasklets pending at ksoftirqd create time. Since, with the RT option to push all softirq code to a thread, any softirqs are defered to this time, it is easy to hit this bug. Clearly only a problem for cpu 0. Here is a patch:

thanks, i've applied this to my -RT tree (will show up in .47-05 and later trees).

Ingo