On Thu, 19 Feb 2015 18:31:05 -0700
Thavatchai Makphaibulchoke <t...@hp.com> wrote:
> This patch fixes the problem that the ownership of a mutex acquired by an
> interrupt handler(IH) gets incorrectly attributed to the interrupted thread.
>
> This could result in an incorrect deadlock detection in function
> rt_mutex_adjust_prio_chain(), causing thread to be killed and possibly leading
> up to a system hang.
>
> Here is the approach taken: when calling from an interrupt handler, instead of
> attributing ownership to the interrupted task, use a reserved task_struct
> value
> to indicate that the owner is a interrupt handler. This approach avoids the
> incorrect deadlock detection.
>
> This also includes changes in several function in rtmutex.c now that the
> lock's
> requester may be a interrupt handler, not a real task struct. This impacts
> the way how the lock is acquired and prioritized and decision whether to do
> the house keeping functions required for a real task struct.
>
> The reserved task_struct values for interrupt handler are
>
> current | 0x2
>
> where current is the task_struct value of the interrupted task.
>
> Since IH will both acquire and release the lock only during an interrupt
> handling, during which current is not changed, the reserved task_struct value
> for an IH should be distinct from another instances of IH on a different cpu.
>
> Kernel version 3.14.25 + patch-3.14.25-rt22
>
> Signed-off-by: T. Makphaibulchoke <t...@hp.com>
OK, I believe I understand the issue. Perhaps it would be much better
to create a fake task per CPU that we use when grabbing locks in
interrupt mode. And make these have a priority of 0 (highest), since
they can not be preempted, they do have such a priority.
Then in the fast trylock and unlock code, we can add:
struct task_struct *curr = current;
if (unlikely(in_irq()))
curr = this_cpu_read(irq_task);
This way the priority inheritance will stop when it hits this task (no
need to boost a task of highest priority), and we can leave that code
alone.
-- Steve
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