Messages in this thread | | | Subject | Any problem if softirq are done in a interrupt context (IRQ stack)? | Date | Wed, 3 Jan 2007 16:23:28 +0800 | From | <> |
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Hello all!
Kernel version : 2.6.18 Arch : i386
With the following conditions, it is possible that softirqs are executed in a interrupt context rather than process one 1) CONFIG_4KSTACKS ----> ON That means the dedicated IRQ stack is used for hardirq handler
2) there exist some Hard IRQ which allows interupt enabled when its handler being executed. That means a possibility that a HARD IRQ handler is interrupted by another one.
3) CONFIG_LOCKDEP ---> OFF Instruction sti will be executed by local_irq_enable_in_hardirq()
Let's suppose the following situation. 1) A process is running without local irq nor bottom half disabled. 2) A hardware interrupt happened. 3) After saving context in process kernel stack, it switch to irq stack. But notice : the preempt_count in irq stack will be zero, because do_irq does not add HARDIRQ_OFFSET to the preept_count. (anyone tell me the reason?)
if (curctx != irqctx) { int arg1, arg2, ebx;
/* build the stack frame on the IRQ stack */ isp = (u32*) ((char*)irqctx + sizeof(*irqctx)); irqctx->tinfo.task = curctx->tinfo.task; irqctx->tinfo.previous_esp = current_stack_pointer;
/* * Copy the softirq bits in preempt_count so that the * softirq checks work in the hardirq context. */ irqctx->tinfo.preempt_count = (irqctx->tinfo.preempt_count & ~SOFTIRQ_MASK) | (curctx->tinfo.preempt_count & SOFTIRQ_MASK);
4) then __do_irq is called, and handle_irq_event is called. Before that, local irq is enabled because the interrupt allow it. 5) during the execution of the hardirq actions, another hardware (depth 2 interrurpt) interrupt happened. 6) SAVE context, and then hardirq handler, during the handler, some softirq is marked 7) when depth 2 interrrupt call irq_exit(), surely do_softirq will be called because in_interrupt return a FALSE. In this point, the stack is still irq stack.
I don't know whether it cause some problem, for example, if some softirq need to make a flag in process control block. Another problem is that softirq handling should have a lower prioirty than hard irq, right?
Thanks for your attention and help.
Regards Zefang
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