[BUG] genirq: Race condition in ONESHOT IRQ handler disabling IRQ forever

On Tue, Feb 07, 2012 at 11:01:06AM +0100, Lothar Wa?mann wrote:

Hi,

quoted

On Mon, Feb 06, 2012 at 09:14:47AM +0100, Lothar Wa?mann wrote:

quoted

Hi,

I already sent this to [off-list ref] on Feb. 1, 2012
but did not get any response there. So resending to a wider audience
with improved subject line:

there is a race condition in the threaded IRQ handler code for oneshot
interrupts that may lead to disabling an IRQ indefinitely. IRQs are
masked before calling the hard-irq handler and are unmasked only after
the soft-irq handler has been run. Thus if the hard-irq handler
returns IRQ_HANDLED instead of IRQ_WAKE_THREAD, meaning the soft-irq
will not be called, the interrupt will remain masked forever.

This can happen due to a short pulse on the interrupt line, that
triggers the interrupt logic, but goes undetected by the hard-irq
handler. The problem can be reproduced with the TSC2007 touch
controller driver that uses ONESHOT interrupts.

Isn't it the responsibility of the driver (say TSC2007)?

In this case, TSC2007 should return IRQ_WAKE_THREAD IMHO.

That would mean it had to return IRQ_WAKE_THREAD unconditionally
making the return code useless.
And it would cause an extra useless loop through the softirq
handler.

Yeah, it's the default behavior when we introduce 'theadirqs',
and it's safe.

You know in your patch unmask_irq() is called locklessly and
it will introduce other race.

Thanks,
Yong