Segfault when calling (Cancelable)Lock.unlock?

[Menno Valkema]

Hi Everyone,

I'm currently using a Nic_connection to exchange data data between
components on linux_x86.

Before sending data from the Nic server I first check whether any data
can be freed. Even before the first packet is send out, using the code
below:

while ( _rx.source()->ack_avail() )
{
  _rx.source()->release_packet( _rx.source()->get_acked_packet() );
}


Whenever I'm sending data out from an extern "C" method (callback passed
to a c library), the application crashes. Looking with GDB, the
issues seems to be with the destructor of the lock guard from the code
from packet_stream.h (full GDB output at the bottom of this email).

bool ready_for_rx()
{
	Genode::Lock::Guard lock_guard(_rx_queue_lock);
	return !_rx_queue->empty();
}

The destructor of the Guard simply calls the unlock method for the lock.
However this crashes. Could it be that the unlock method throws an
exception in the destructor, or that there might be uninitialized
variables within the lock itself?

I'm sort of lost here, because I've used the Nic_connection in similar
settings in the past (also called from an extern "C" context as a c code
callback). However this time it consistently breaks, whenever I try to
sent out the first packet from an extern "c" context (it does work when
sending the packet out from normal c++ code.

Any suggestions what might causes the crash in my application?

Cheers, Menno



Program received signal SIGSEGV, Segmentation fault.
0x0000000001143c22 in ~Lock_guard (this=<optimized out>,
__in_chrg=<optimized out>)
    at <project-path...>/repos/base/include/base/lock_guard.h:42
42			~Lock_guard() { _lock.unlock(); }
(gdb) bt
#0  0x0000000001143c22 in ~Lock_guard (this=<optimized out>,
__in_chrg=<optimized out>)
    at <project-path...>/repos/base/include/base/lock_guard.h:42
#1  ready_for_rx (this=<optimized out>) at
<project-path...>/repos/os/include/os/packet_stream.h:400
#2  ack_avail (this=<optimized out>) at
<project-path...>/repos/os/include/os/packet_stream.h:686


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