[erlang-questions] [erlang-bugs] erts_port[].drv_ptr == 0, when erts_port[].status not free

[Rickard Green]

Hi Paul,

Thanks for the bug report. The attached patch should fix the problem. 
This fix will be included in R12B-4.

How to apply the patch:
   $ gtar -zxf otp_src_R12B-3.tar.gz
   $ gpatch -ZNp0 < OTP-7464.patch
   patching file otp_src_R12B-3/erts/emulator/beam/io.c
   $ # Build and install as usual

BR,
Rickard Green, Erlang/OTP, Ericsson AB.

Raimo Niskanen wrote:
> Thank you for your bug report.
> 
> We will look into your problem when the concerned developers
> comes in after their vacation.
> 
> Can you give us host OS and Erlang release too?
> 
> 
> 
> On Tue, Jul 01, 2008 at 07:24:05PM -0500, Paul Fisher wrote:
>> We have a system where we run lots of linked-in driver ports that get
>> created/used/closed frequently and sometimes very quickly.  Today when
>> several open_port/2, port_command/2 and port_close/1 cycles happened
>> rapid succession, a SIGSEGV occurrect in erl_bif_ddl.c:
>>
>> Program received signal SIGSEGV, Segmentation fault.
>> [Switching to Thread 1125235040 (LWP 12087)]
>> 0x0000000000449712 in erl_ddll_try_unload_2 (p=0x2aaaab11fc90,
>>     name_term=659339, options=46912503328425) at beam/erl_bif_ddll.c:592
>>
>> The emulator was run on a Q6600 (quad-core, 2.4Ghz), and started with +A
>> 8,
>> and the linked-in driver executes the bulk of its work with
>> driver_async().
>> There were continuously 8 driver cycles running for 5-10 seconds before
>> the
>> segfault occurred.
>>
>> ???(gdb) where
>> #0  0x0000000000449712 in erl_ddll_try_unload_2 (p=0x2aaaab11fc90,
>>     name_term=659339, options=46912503328425) at beam/erl_bif_ddll.c:592
>> #1  0x000000000052337f in process_main () at beam/beam_emu.c:2073
>> #2  0x000000000049c213 in sched_thread_func (vesdp=0x2ae18cb74f98)
>>     at beam/erl_process.c:741
>> #3  0x00000000005b6818 in thr_wrapper (vtwd=0x7fff1eb77de0)
>>     at common/ethread.c:474
>> #4  0x00002ae18c530f1a in start_thread () from /lib/libpthread.so.0
>> #5  0x00002ae18c8135d2 in clone () from /lib/libc.so.6
>> #6  0x0000000000000000 in ?? ()
>>
>> So the code at the point of the SIGSEGV @ erl_bif_ddll.c:592 says:
>>
>>         for (j = 0; j < erts_max_ports; j++) {
>> =>          if (!(erts_port[j].status &  FREE_PORT_FLAGS)
>>                 && erts_port[j].drv_ptr->handle == dh) {
>>
>> It appears that the code assumes that if the erts_port array entry being
>> evaluated during the search has a valid (non-zero) drv_ptr value, if the
>> entry is not marked as free.  At the time of the crash, this is clearly
>> not
>> the case:
>>
>> (gdb) p j
>> $8 = 896
>>
>> (gdb) p erts_port[j]
>> $7 = {sched = {next = 0x0, prev = 0x0, taskq = 0x0, exe_taskq = 0x0},
>>   timeout_task = {counter = 0}, refc = {counter = 2}, lock = 0x81b3c8,
>>   xports = 0x0, id = 14343, connected = 0, caller = 0, data = 0, bp =
>> 0x0,
>>   nlinks = 0x0, monitors = 0x0, bytes_in = 0, bytes_out = 0, ptimer =
>> 0x0,
>>   tracer_proc = 18446744073709551611, trace_flags = 0, ioq = {size = 0,
>>     v_start = 0x0, v_end = 0x0, v_head = 0x0, v_tail = 0x0, v_small = {{
>>         iov_base = 0x0, iov_len = 0}, {iov_base = 0x0, iov_len = 0}, {
>>         iov_base = 0x0, iov_len = 0}, {iov_base = 0x0, iov_len = 0}, {
>>         iov_base = 0x0, iov_len = 0}}, b_start = 0x0, b_end = 0x0,
>>     b_head = 0x0, b_tail = 0x0, b_small = {0x0, 0x0, 0x0, 0x0, 0x0}},
>>   dist_entry = 0x0, name = 0x0, drv_ptr = 0x0, drv_data = 0, suspended =
>> 0x0,
>>   linebuf = 0x0, status = 4096, control_flags = 0, reg = 0x0,
>>   port_data_lock = 0x0}
>>
>> (gdb) p erts_port[j].drv_ptr
>> $6 = (ErlDrvEntry *) 0x0
>>
>>
>> So the real questions are: 1) is whether the assumption built into this
>> code is correct; and 2) if so, how did we get in the position of
>> violating
>> it.  I'd appreciate some insight into what could be going on here, and
>> where I should can start looking.
>>
>>
>> -- 
>> paul
>>
>> _______________________________________________
>> erlang-bugs mailing list
>> erlang-bugs@REDACTED
>> http://www.erlang.org/mailman/listinfo/erlang-bugs
> 
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