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Date: Wed, 17 Jul 2019 11:08:55 +0200
From: Marek Majkowski <marek@...udflare.com>
To: malc <mlashley@...il.com>
Cc: vyasevich@...il.com, nhorman@...driver.com,
marcelo.leitner@...il.com, Linux SCTP <linux-sctp@...r.kernel.org>,
netdev@...r.kernel.org, kernel-team <kernel-team@...udflare.com>
Subject: Re: OOM triggered by SCTP
Malc, thanks taking a look.
I'm able to trigger the problem on non-SMP virtme with 4GiB ram, but
I'm not able to trigger it on my SMP host with 16GiB.
The slab info from dmesg (on 4GiB run):
Unreclaimable slab info:
SCTPv6 31068KB 31068KB
sctp_chunk 24321KB 24990KB
sctp_bind_bucket 972KB 972KB
skbuff_head_cache 28484KB 29051KB
kmalloc-8k 82KB 148KB
kmalloc-4k 81897KB 82943KB
kmalloc-2k 314KB 382KB
kmalloc-1k 27446KB 29547KB
kmalloc-512 30312KB 30915KB
The biggest issue is that the OOM is often unrecoverable:
---[ end Kernel panic - not syncing: System is deadlocked on memory ]---
Out of memory and no killable processes...
Kernel panic - not syncing: System is deadlocked on memory
I noticed sctp_mem toggle. Would tweaking it change anything?
net.sctp.sctp_mem = 80976 107969 161952
net.sctp.sctp_rmem = 4096 865500 3455008
net.sctp.sctp_wmem = 4096 16384 3455008
For the record, stuffing "shutdown(sd, SHUT_RDWR)" before the "close"
doesn't solve the problem.
Marek
On Wed, Jul 17, 2019 at 1:59 AM malc <mlashley@...il.com> wrote:
>
> On Tue, Jul 16, 2019 at 10:49 PM Marek Majkowski <marek@...udflare.com> wrote:
> >
> > Morning,
> >
> > My poor man's fuzzer found something interesting in SCTP. It seems
> > like creating large number of SCTP sockets + some magic dance, upsets
> > a memory subsystem related to SCTP. The sequence:
> >
> > - create SCTP socket
> > - call setsockopts (SCTP_EVENTS)
> > - call bind(::1, port)
> > - call sendmsg(long buffer, MSG_CONFIRM, ::1, port)
> > - close SCTP socket
> > - repeat couple thousand times
> >
> > Full code:
> > https://gist.github.com/majek/bd083dae769804d39134ce01f4f802bb#file-test_sctp-c
> >
> > I'm running it on virtme the simplest way:
> > $ virtme-run --show-boot-console --rw --pwd --kimg bzImage --memory
> > 512M --script-sh ./test_sctp
> >
> > Originally I was running it inside net namespace, and just having a
> > localhost interface is sufficient to trigger the problem.
> >
> > Kernel is 5.2.1 (with KASAN and such, but that shouldn't be a factor).
> > In some tests I saw a message that might indicate something funny
> > hitting neighbor table:
> >
> > neighbour: ndisc_cache: neighbor table overflow!
> >
> > I'm not addr-decoding the stack trace, since it seems unrelated to the
> > root cause.
> >
> > Cheers,
> > Marek
>
> I _think_ this is an 'expected' peculiarity of SCTP on loopback - you
> test_sctp.c ends up creating actual associations to itself on the same
> socket (you can test safely by reducing the port range (say
> 30000-32000) and setting the for-loop-clause to 'run < 1')
> You'll see a bunch of associations established like the following
> (note that I(kernel) was dropping packets for this capture - even with
> /only/ 2000 sockets used...)
>
> $ tshark -r sctp.pcap -Y 'sctp.assoc_index==4'
> 21 0.000409127 ::1 → ::1 SCTP INIT
> 22 0.000436281 ::1 → ::1 SCTP INIT_ACK
> 23 0.000442106 ::1 → ::1 SCTP COOKIE_ECHO
> 24 0.000463007 ::1 → ::1 SCTP COOKIE_ACK DATA
> (Message Fragment)
> presumably your close()
> happens here and we enter SHUTDOWN-PENDING, where we wait for pending
> data to be acknowledged, I'm not convinced that we shouldn't be
> SACK'ing the data from the 'peer' at this point - but for whatever
> reason, we aren't.
> We then run thru
> path-max-retrans, and finally ABORT (the abort indication also shows
> the PMR-exceeded indication in the 'Cause Information')
> 25 0.000476083 ::1 → ::1 SCTP SACK
> 13619 3.017788109 ::1 → ::1 SCTP DATA (retransmission)
> 14022 3.222690889 ::1 → ::1 SCTP SACK
> 18922 21.938217449 ::1 → ::1 SCTP SACK
> 33476 69.831029904 ::1 → ::1 SCTP HEARTBEAT
> 33561 69.831310796 ::1 → ::1 SCTP HEARTBEAT_ACK
> 40816 94.102667600 ::1 → ::1 SCTP SACK
> 40910 95.942741287 ::1 → ::1 SCTP DATA (retransmission)
> 41039 96.152023010 ::1 → ::1 SCTP SACK
> 41100 100.182685237 ::1 → ::1 SCTP SACK
> 41212 108.230746764 ::1 → ::1 SCTP DATA (retransmission)
> 41345 108.439061392 ::1 → ::1 SCTP SACK
> 41407 116.422688507 ::1 → ::1 SCTP HEARTBEAT
> 41413 116.423183124 ::1 → ::1 SCTP HEARTBEAT_ACK
> 41494 124.823749255 ::1 → ::1 SCTP SACK
> 41576 126.663648718 ::1 → ::1 SCTP ABORT
>
> With your entire 512M - you'd only have about 16KB for each of these
> 31K associations tops, I suspect that having a 64KB pending data chunk
> (fragmented ULP msg) for each association for >= 90s is what is
> exhausting memory here - although I'm sure Neil or Michael will be
> along to correct me ;-)
>
> What's interesting - as you reduce the payload size - we end up
> bundling DATA from the 'initiator' side (in COOKIE ECHO) - and
> everything works as expected... (the SACK here is for the bundled DATA
> chunks TSN.
>
> mlashley@...lity /tmp $ tshark -r /tmp/sctp_index4_10K.pcap
> 1 0.000000000 ::1 → ::1 SCTP INIT
> 2 0.000014491 ::1 → ::1 SCTP INIT_ACK
> 3 0.000024190 ::1 → ::1 SCTP COOKIE_ECHO DATA
> 4 0.000034833 ::1 → ::1 SCTP COOKIE_ACK
> 5 0.000040646 ::1 → ::1 SCTP SACK
> 6 0.000050287 ::1 → ::1 SCTP ABORT
>
> In short - the SCTP associations /can/ persist after user-space calls
> close() whilst there is outstanding data (for path.max.retrans *
> rto-with-doubling[due to T3-rtx expiry])
>
> (My tests on 5.2.0 as it is what I had to hand...)
>
> Cheers,
> malc.
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