context[2] stuck: (null)

[Arkady]

Update. The failure happens consistently in the same context

"context[1] stuck: (null), line_get=36848, line_put=36914
last_err=(null) last_stmt=identifier 'probe_begin'"
where line_get and line_put are lines in the enter_be_probe()

36843     #endif
36844     goto probe_epilogue;
36845   }
36846   if (atomic_read (session_state()) != stp->state)
36847     goto probe_epilogue;
36848   c = _stp_runtime_entryfn_get_context(__LINE__);
36849   if (!c) {
36850     #if !INTERRUPTIBLE
36851     atomic_inc (skipped_count());
36852     #endif
36853     #ifdef STP_TIMING
36854     atomic_inc (skipped_count_reentrant());
36855     #endif
36856     goto probe_epilogue;
36857   }
..................
36907     }
36908   }
36909 probe_epilogue:
36910   if (unlikely (atomic_read (skipped_count()) > MAXSKIPPED)) {
36911     if (unlikely (pseudo_atomic_cmpxchg(session_state(),
STAP_SESSION_RUNNING, STAP_SESSION_ERROR) == STAP_SESSION_RUNNING))
36912     _stp_error ("Skipped too many probes, check MAXSKIPPED or
try again with stap -t for more details.");
36913   }
36914   _stp_runtime_entryfn_put_context(c, __LINE__);
36915   #if !INTERRUPTIBLE
36916   local_irq_restore (flags);
36917   #endif
36918   #endif // STP_ALIBI

On Mon, Jul 10, 2017 at 6:16 PM, Arkady <arkady.miasnikov@gmail.com> wrote:
> Hi,
>
> I am getting context[2] stuck: (null) error. The cause of error is
> likely the "unmanaged" code I have added to the driver. Specifically I
> have a shared memory (mmap) in the driver. The failure happens
> randomly every 50-200 module restarts The failure happens only on the
> multicore CPUs, or happens often enough to be caught.
>
> I tried to force the the wait function with
> STAP_OVERRIDE_STUCK_CONTEXT - kernel panics in one of the (probably
> random) probes.
>
> While debugging the issue I  patched the SystemTap source code - added
> an argument to the _stp_runtime_entryfn_get_context(int) like in this
> commit https://github.com/larytet/SystemTap/commit/61a284732893fa6f201e07f9f12f5e1820e7c26f
> In the function _stp_runtime_context_wait() I print the line in the
> source code which called the _stp_runtime_entryfn_get_context()
>
> The "bad" context is enter_be_probe(). I checked the source code of
> enter_be_probe() and there is not much there.
>
> I struggle with the problem for some time and I will greatly
> appreciate any tip.
>
> Thank you, Arkady.