Re: IRQ Tracing Problem in Linux 2.6.28 Kernel
Jeffrey Cao <jcao.linux <at> gmail.com>
2009-04-24 15:50:45 GMT
On 2009-04-13, Sol Kavy <skavy <at> ubicom.com> wrote:
> The following back trace represents a deadlock in Ubicom's SMP port of 2.6.28 kernel. I am sure that we
are doing something unexpected. I would appreciate the community's help in understanding what is
> Thanks in advance for any pointers,
> Sol Kavy
> Ubicom's initial port does not use GENERIC_CLOCKEVENTS. Instead it uses a periodic timer based on HZ. The
periodic timer calls do_timer() on each tick.
> From the arch directory perspective, we are required to hold the xtime_lock before calling
do_timer(). The lock is indeed help by cpu 3 as evidenced in the output below.
> The call to get_jiffies_64() at the top of the backtrace is attempting to read the jiffies in a reliable
fashion. The caller is required to wait for the xtime_lock not to be held. Clearly, since we are in a
path that is holding the xtime_lock, this will never make forward progress.
For x86 arch, function get_jiffies_64() seems not to wait the xtime_lock,
but to do something related to CPU ordering:
|->alternative("lock; addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2)
I'm not sure if this is the same as to accquire xtime_lock spinlock. Maybe this
is a point you need check.