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SubjectRe: [PATCH 3/3] do_exit(): do not panic if exiting thread is not serving an interrupt
On Mon, 19 Mar 2012, Alexander Gordeev wrote:

> Currently a crashed and killed forced oneshot threaded handler hits
> in_interrupt() check in do_exit() and panics. As result, the code that
> cleans up IRQ descriptor never not get called and IRQ line stays masked.
>
> Similarly non-forced oneshot threaded handlers that crashed while holding
> bh lock leave a IRQ line masked.
>
> Regular threaded handlers that crashed while holding bh simply panic,
> although they could have just terminate loudly.
>
> This fix allows IRQ threaded handlers get killed gracefully instead of
> panicking.
>
> Since introduction of SOFTIRQ_DISABLE_OFFSET in 75e1056 we can differ
> between bh being serviced and bh being disabled. Use this ability to
> avoid unnecessary crashes when a exiting thread explicitly disabled bh
> and is not serving any softirq. Still we will get the regular warning
> that exiting thread is in atomic context.

Hmm, this applies for all threads which exit with bh disabled. We risk
data corruption this way as the crash of a task might happen within a
data set manipulation protected by bh_disable.

Not sure whether the chance to get debug information from the machine
is worth the risk of data corruption causes follow up problems.

Thanks,

tglx


> Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
> ---
> include/linux/hardirq.h | 4 ++++
> kernel/exit.c | 2 +-
> 2 files changed, 5 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
> index bb7f309..93aca12 100644
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -82,11 +82,15 @@
> * Are we in a softirq context? Interrupt context?
> * in_softirq - Are we currently processing softirq or have bh disabled?
> * in_serving_softirq - Are we currently processing softirq?
> + * in_serving_interrupt - Are we currently processing softirq, nmi or
> + * hardware interrupt?
> */
> #define in_irq() (hardirq_count())
> #define in_softirq() (softirq_count())
> #define in_interrupt() (irq_count())
> #define in_serving_softirq() (softirq_count() & SOFTIRQ_OFFSET)
> +#define in_serving_interrupt() (preempt_count() & (HARDIRQ_MASK \
> + | SOFTIRQ_OFFSET | NMI_MASK))
>
> /*
> * Are we in NMI context?
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 752d2c0..0c78ae6 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -896,7 +896,7 @@ void do_exit(long code)
>
> WARN_ON(blk_needs_flush_plug(tsk));
>
> - if (unlikely(in_interrupt()))
> + if (unlikely(in_serving_interrupt()))
> panic("Aiee, killing interrupt handler!");
> if (unlikely(!tsk->pid))
> panic("Attempted to kill the idle task!");
> --
> 1.7.7.6
>
>
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