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

    > On Mon, Feb 06, 2012 at 09:14:47AM +0100, Lothar Waßmann wrote:
    > > Hi,
    > >
    > > I already sent this to <linux-kernel@vger.kernel.org> 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.


    Lothar Waßmann
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