Hi, Flavio.
On 11/24/21 10:16, Flavio Leitner wrote:
On Tue, Nov 23, 2021 at 07:58:52PM -0300, Murilo Opsfelder Araújo wrote:
Hi, Flavio.
On 11/23/21 15:32, Flavio Leitner wrote:
On Mon, Nov 22, 2021 at 03:46:28PM -0300, Murilo Opsfelder Araújo wrote:
Hi, Ilya Maximets.
On 11/19/21 13:23, Ilya Maximets wrote:
On 11/18/21 22:19, David Christensen wrote:
On 11/18/21 11:56 AM, Murilo Opsfelder Araújo wrote:
On 11/16/21 19:31, Ilya Maximets wrote:
On 10/25/21 19:45, David Christensen wrote:
In certain high load situations, such as when creating a large number of
ports on a switch, the parameter 'sock' may be passed to nl_sock_recv__()
as null, resulting in a segmentation fault when 'sock' is later
dereferenced, such as when calling recvmsg().
Hi, David. Thanks for the patch.
It's OK to check for a NULL pointer there, I guess. However,
do you know from where it was actually called? This function,
in general, should not be called without the actual socket,
so we, probably, should fix the caller instead.
Best regards, Ilya Maximets.
Hi, Ilya Maximets.
When I looked at the coredump file, ch->sock was nil and was passed to
nl_sock_recv():
(gdb) l
2701
2702 while (handler->event_offset < handler->n_events) {
2703 int idx = handler->epoll_events[handler->event_offset].data.u32;
2704 struct dpif_channel *ch = &dpif->channels[idx];
(gdb) p idx
$26 = 4
(gdb) p *dpif->channels@5
$27 = {{sock = 0x1001ae88240, last_poll = -9223372036854775808}, {sock =
0x1001aa9a8a0, last_poll = -9223372036854775808}, {sock = 0x1001ae09510,
last_poll = 60634070}, {sock = 0x1001a9dbb60, last_poll = 60756950}, {sock =
0x0,
last_poll = 61340749}}
The above snippet is from lib/dpif-netlink.c and the caller is
dpif_netlink_recv_vport_dispatch().
The channel at idx=4 had sock=0x0, which was passed to nl_sock_recv() via
ch->sock parameter.
In that function, it tried to access sock->fd when calling recvmsg(), causing
the segfault.
I'm not enough experienced in Open vSwitch to explain why sock was nil at that
given index.
The fix seems worth, though.
A few other points of note:
- Test system was a very large configuration (2K CPUs, > 1TB RAM)
- OVS Switch was configured with 6K ports as follows:
# b=br0; cmds=; for i in {1..6000}; do cmds+=" -- add-port $b p$i -- set interface
p$i type=internal"; done
# time sudo ovs-vsctl $cmds
- OVS was installed from RHEL RPM. Build from source did not exhibit the same
problem.
- Unable to reproduce on a different system (128 CPUs, 256GB RAM), even with
10K ports.
Dave
Thanks for all the information. Having a NULL socket in the 'channels'
array doesn't look a good sign. This may mean that even if OVS will
not crash, it may not receive upcalls for certain ports, which is not
good eihter.
Could you provide more info on which RHEL package did you use and which
version you built from source? Maybe we can find the difference.
When the bug was reported internally, the distro package was actually from
Fedora 33 ppc64le.
One difference I've found at that time was regarding the configure options.
From the logs at [0], the distro package was configured with these options:
+ ./configure --build=ppc64le-redhat-linux-gnu
--host=ppc64le-redhat-linux-gnu --program-prefix= --disable-dependency-tracking
--prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin
--sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include
--libdir=/usr/lib64 --libexecdir=/usr/libexec --localstatedir=/var
--sharedstatedir=/var/lib --mandir=/usr/share/man --infodir=/usr/share/info
--enable-libcapng --disable-static --enable-shared --enable-ssl
--with-dpdk=shared --with-pkidir=/var/lib/openvswitch/pki
And the built-from-source binaries from Dave were built like this:
git clone https://github.com/openvswitch/ovs.git
cd ovs/
git checkout v2.15.0
Do you mean 2.16.0? Because the dpif_netlink_recv_vport_dispatch()
from the snippet above doesn't exist in 2.15.0.
And the FC33 uses 2.15.0:
https://koji.fedoraproject.org/koji/buildinfo?buildID=1713250
I'm sorry. I'd looked into the wrong revision.
The correct name of the caller is dpif_netlink_recv__(), in lib/dpif-netlink.c.
The version tag is correct: v2.15.0
It matches the version from Fedora 33.
OK, that makes sense.
Can you reproduce the issue?
The reason I am asking is because in 2.16.0 we added another way to
handle upcalls, so I am wondering if the bug was introduced with
that change 2.16.0 or if it was already there in 2.15.0.
The system where this issue happened is being used for other purposes now.
I'll see if we can manage to reproduce on another one.
At least we know if there is a bug, it's prior to the big change
adding the new upcall dispatching.
We may also want to use latest bits of OVS and Fedora.
Also, could you provide the full backtrace of all threads?
(gdb) thread apply all bt
It would be nice to have a dump of the struct handler too.
Absolutely! We'll make sure to capture these data next time.
That might be available in the core you already have.
Actually, if you can put the core somewhere maybe I can
take a look here using fedora debuginfo package.
fbl
I just wanted to let you know that I tried Open vSwitch at commit
commit 1f5749c790accd98dbcafdaefc40bf5e52d7c672 ("flow: Consider dataofs when
parsing TCP packets.")
on a different system (a KVM guest) and I wasn't able to reproduce the issue on
that system.
I also tried using Fedora 35 package openvswitch-2.15.0-7.fc35.ppc64le but the
issue didn't manifest either.
If we happen to hit the problem again on the larger system (the one with 1TB of
RAM), I'll let you know and will capture requested data.
Thanks a lot for your help! We did appreciate!
Cheers!
--
Murilo
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