From: Zachary Amsden Date: Thu, 7 Dec 2006 04:39:39 +0000 (-0800) Subject: [PATCH] softirq: remove BUG_ONs which can incorrectly trigger X-Git-Tag: v2.6.20-rc1~145^2^2~77 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3908fd2ed920af818aa596672da68ba26173ff27;p=linux-2.6 [PATCH] softirq: remove BUG_ONs which can incorrectly trigger It is possible to have tasklets get scheduled before softirqd has had a chance to spawn on all CPUs. This is totally harmless; after success during action CPU_UP_PREPARE, action CPU_ONLINE will be called, which immediately wakes softirqd on the appropriate CPU to process the already pending tasklets. So there is no danger of having a missed wakeup for any tasklets that were already pending. In particular, i386 is affected by this during startup, and is visible when using a very large initrd; during the time it takes for the initrd to be decompressed, a timer IRQ can come in and schedule RCU callbacks. It is also possible that resending of a hardware IRQ via a softirq triggers the same bug. Because of different timing conditions, this shows up in all emulators and virtual machines tested, including Xen, VMware, Virtual PC, and Qemu. It is also possible to trigger on native hardware with a large enough initrd, although I don't have a reliable case demonstrating that. Signed-off-by: Zachary Amsden Cc: Cc: Ingo Molnar Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/softirq.c b/kernel/softirq.c index bf25015dce..918e52df09 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -574,8 +574,6 @@ static int __cpuinit cpu_callback(struct notifier_block *nfb, switch (action) { case CPU_UP_PREPARE: - 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);