On Thu, 19 Feb 2015 18:31:05 -0700 Thavatchai Makphaibulchoke <tmac@xxxxxx> 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 <tmac@xxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
