On Thu, Jun 10, 2004 at 10:40:32 +0200, Jan Hudec wrote: > The key thing to note is, that spinlock does a busy waiting. Something > like "while(lock);" (careful crafting in assembly is necessary for it to > work, of course). So only the other CPU on SMP can ever release it > (that's why spinlocks compile to nothing in non-preemptable UP kernel). > > If interrupt handler ever need the lock, you need the > _irqsave/_irqrestore variant, which clears interrupt flag. So the > interrut simply can't happen when the lock is held. > > Note however, that many functions are not called from interrupt, but > rather from scheduler -- and that won't run when you are in kernel mode > unless you call schedule(). (In preemptable kernel it might happen, but > holding spinlock prevents preemption.) Sorry for replying to myself, but I forgot about one thing. There is the spin_lock_bh/spin_unlock_bh variant, that does not disable interrupts, but does disable bottom-halves. Not really sure where exactly the difference lies, but I believe it's appropriate for most hooks. ------------------------------------------------------------------------------- Jan 'Bulb' Hudec <bulb@ucw.cz>
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