Re: [PATCH v3] tgtd: refresh ready fds of event loop after event deletion

At Tue, 4 Mar 2014 17:14:41 +0200,
Or Gerlitz wrote:
> 
> On 26/02/2014 07:13, Hitoshi Mitake wrote:
> > For example, we can produce segfault of tgtd under heavy load. Below
> > is a backtrace obtained from the core file:
> >   (gdb) bt
> >   #0  0x0000000000000000 in ?? ()
> >   #1  0x0000000000411419 in event_loop () at tgtd.c:414
> >   #2  0x0000000000411b65 in main (argc=<value optimized out>, argv=<value optimized out>) at tgtd.c:591
> >
> > To be honest, I still don't find an event handler which calls
> > tgt_event_del() for other fds. But with this modification, the above
> > segfault is avoided. The change seems to be effective.
> 
> Just want to make sure I follow --- you do have a way to reproduce the 
> bug, but from code inspection you didn't find an event handler in tgt 
> which calls  tgt_event_del() for "other" fds which is the trigger for 
> the bug, right?

Yes. To be more precise, I'd like to describe my understanding:

1. There are some event handlers which can close "other
fds". e.g. mtask_recv_send_handler(). It can be invoked via input of
unix domain socket and close fds of tcp connections when user invokes
"--op delete --mode target".

2. But we can produce the above segfault without using it...

> 
> Can you please provide the steps to reproduce the bug?

We are using 4 node cluster connected via 10Gbps ethernet. 1 node
executes tgtd for providing iSCSI target. The backing store is
sheepdog. All nodes execute 4 VMs and read iso file (about 4GB) from
single logical unit.

# The test is mocking an environment of thin clients. We need multiple
# dd processes for exhausting the 10Gbps network.

When we run the above test several times, the segfault occurs. But, of
course, we don't invoke the "tgtadm --op delete --mode target" during
the testing.

Thanks,
Hitoshi