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[PATCH] softirq: remove BUG_ONs which can incorrectly trigger

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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 <zach@vmware.com>
Cc: <caglar@pardus.org.tr>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Zachary Amsden 2006-12-06 20:39:39 -08:00 committed by Linus Torvalds
parent c949d4eb40
commit 3908fd2ed9
1 changed files with 0 additions and 2 deletions
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2
kernel/softirq.c
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@ -574,8 +574,6 @@ static int __cpuinit cpu_callback(struct notifier_block *nfb,
switch (action) { switch (action) {
case CPU_UP_PREPARE: 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); p = kthread_create(ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
if (IS_ERR(p)) { if (IS_ERR(p)) {
printk("ksoftirqd for %i failed\n", hotcpu); printk("ksoftirqd for %i failed\n", hotcpu);