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SubjectRe: Race condition in 2.4 tasklet handling (cli() broken?)
 Additional suspicious things.

1. tasklet_kill() has similar race condition. mb() required before

2. local_bh_count() and global_bh_lock tests inside wait_on_irq()
suggests that cli() tries to block not only interrupt handling but all
softirq handlings of all cpus; however, current implementation does
not guarantee that.

Because local_bh_count is adjusted in do_softirq() _after_
decrementing local_irq_count(), other cpus may happily begin
softirq/tasklet/bh handling while a cpu is inside cli() - sti()
critical section.

If softirq handling is not guaranteed to be blocked during cli() -
sti() critical section, local_bh_count() and global_bh_lock tests
inside wait_on_irq() are redundant, and if it should be guranteed,
current implementation seems broken.

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