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. *blink* > > 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. I highly doubt this is an incorrect deadlock that was detected. My money is on a real deadlock that happened. > > 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. How is this an incorrect deadlock? Please explain. > > 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. > The interrupt handler is a thread just like any other task. It's not special. If there was a deadlock detected, it most likely means that a deadlock exists. -- Steve > Kernel version 3.14.25 + patch-3.14.25-rt22 > > Signed-off-by: T. Makphaibulchoke <tmac@xxxxxx> > --- > include/linux/spinlock_rt.h | 4 + > kernel/locking/rtmutex-debug.c | 15 ++- > kernel/locking/rtmutex.c | 212 ++++++++++++++++++++++++++++------------ > kernel/locking/rtmutex_common.h | 21 ++++ > kernel/timer.c | 4 +- > 5 files changed, 188 insertions(+), 68 deletions(-) > -- 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
