[TS-3970] Core in PluginVC

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Invalid
• Labels: crash
• Assignee: Susan Hinrichs
• Reporter: Susan Hinrichs
• Created: 15/Oct/15 15:32
• Updated: 13/Jan/16 06:06
• Resolved: 11/Nov/15 17:08

Description

One of our plugins moving from 5.0.1 to 5.3.x (plus 6.0 backports) started seeing the following stack trace with high frequency.

Program terminated with signal 11, Segmentation fault.
#0 0x000000000054c232 in PluginVC::process_read_side (this=0x2b9ace2f3850, other_side_call=true) at PluginVC.cc:638
in PluginVC.cc
#0 0x000000000054c232 in PluginVC::process_read_side (this=0x2b9ace2f3850, other_side_call=true) at PluginVC.cc:638
#1 0x000000000054be2a in PluginVC::process_write_side (this=0x2b9ace2f3a40, other_side_call=false) at PluginVC.cc:555
#2 0x000000000054acdb in PluginVC::main_handler (this=0x2b9ace2f3a40, event=1, data=0x2b9b1e32e930) at PluginVC.cc:208
#3 0x0000000000510c84 in Continuation::handleEvent (this=0x2b9ace2f3a40, event=1, data=0x2b9b1e32e930) at ../iocore/eventsystem/I_Continuation.h:145
#4 0x000000000079a2a6 in EThread::process_event (this=0x2b9ab63d9010, e=0x2b9b1e32e930, calling_code=1) at UnixEThread.cc:128
#5 0x000000000079a474 in EThread::execute (this=0x2b9ab63d9010) at UnixEThread.cc:179
#6 0x0000000000799851 in spawn_thread_internal (a=0x2fea360) at Thread.cc:85
#7 0x00002b9ab457e9d1 in start_thread () from /lib64/libpthread.so.0
#8 0x00000030d38e88fd in clone () from /lib64/libc.so.6

The output buffer fetched by PluginVC::process_read_side was NULL.

I think they reason this appears in 5.3 is due to the fix for TS-3522. Before that change only one do_io_read was made very early to set up the read from server. This bug fix delays the real read to later and pulls mbuf out of server_buffer_reader. In some cases for this plugin, the mbuf is NULL by the time we get there.

I fixed the core by using server_session->read_buffer in the do_io_read instead of server_buffer_reader->mbuf. This seems to fix the problem.