[Bug network/13904] New: getaddrinfo does two identical queries, breaks dns round robin with two hosts

[Bug network/13904] New: getaddrinfo does two identical queries, breaks dns round robin with two hosts

[kjp at ci dot uchicago.edu]

http://sourceware.org/bugzilla/show_bug.cgi?id=13904

             Bug #: 13904
           Summary: getaddrinfo does two identical queries, breaks dns
                    round robin with two hosts
           Product: glibc
           Version: 2.11
            Status: NEW
          Severity: normal
          Priority: P2
         Component: network
        AssignedTo: unassigned@sourceware.org
        ReportedBy: kjp@ci.uchicago.edu
    Classification: Unclassified


The host 'gridftp.nautilus.nics.xsede.org' has two ipv4 ips.  when using ping,
each ping execution alternates hosts, and strace shows only one dns query is
sent.  

however, another program using getaddrinfo() does not get the same rotation. 
It appears that getaddrinfo inexplicably sends a redundant dns query (only
thing different is transaction id), thus causing an entire rotation through
both hosts each time.  The returned ip will always be fairly constant - it will
be the last ip that 'ping' got.   So, if a host has a power of 2 number of ips,
rotation is broken.. particularly badly if there are only two ips total.

note: nscd is not running, and it does not appear to fix the problem

test program:

int main(void)
{
    struct addrinfo *result;
    struct addrinfo *res;
    int error;

   /* nautilus has two hosts, we want to pick a random
     * one.  
     * Note: problem occurs with or without final trailing '.' */
    error = getaddrinfo("gridftp.nautilus.nics.xsede.org",
            NULL, NULL, &result);
    // sent two DNS queries, which breaks rotation of two ips
    // first ip result is always the same ip, even though nameserver is
reordering each response

strace of c program:

strace -s 100 -e sendto ./a.out 
sendto(3, "\24\0\0\0\26\0\1\3\276\301pO\0\0\0\0\0\0\0\0", 20, 0,
{sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 20
sendto(3,
"\360\342\1\0\0\1\0\0\0\0\0\0\7gridftp\10nautilus\4nics\5xsede\3org\0\0\1\0\1",
49, MSG_NOSIGNAL, NULL, 0) = 49
sendto(3,
"\2654\1\0\0\1\0\0\0\0\0\0\7gridftp\10nautilus\4nics\5xsede\3org\0\0\1\0\1",
49, MSG_NOSIGNAL, NULL, 0) = 49

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug network/13904] getaddrinfo does two identical queries, breaks dns round robin with two hosts

[kjp at ci dot uchicago.edu]

http://sourceware.org/bugzilla/show_bug.cgi?id=13904

--- Comment #1 from kjp at ci dot uchicago.edu 2012-03-26 20:00:54 UTC ---
I'm also getting the same behavior on the latest ubuntu 12.04 beta:

GNU C Library (Ubuntu EGLIBC 2.15-0ubuntu6) stable release version 2.15, by
Roland McGrath et al.
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 4.6.3.
Compiled on a Linux 3.2.12 system on 2012-03-21.
Available extensions:
    crypt add-on version 2.1 by Michael Glad and others
    GNU Libidn by Simon Josefsson
    Native POSIX Threads Library by Ulrich Drepper et al
    BIND-8.2.3-T5B
libc ABIs: UNIQUE IFUNC

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug network/13904] getaddrinfo does two identical queries, breaks dns round robin with two hosts

[kjp at ci dot uchicago.edu]

http://sourceware.org/bugzilla/show_bug.cgi?id=13904

--- Comment #2 from kjp at ci dot uchicago.edu 2012-03-27 16:28:06 UTC ---
This doesn't seem to happen on fedora 15, so maybe it's eglibc specific.  I'm
reporting it there.

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug network/13904] getaddrinfo does two identical queries, breaks dns round robin with two hosts

[jvb127 at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=13904

Jeroen van Bemmel <jvb127 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jvb127 at gmail dot com

--- Comment #3 from Jeroen van Bemmel <jvb127 at gmail dot com> 2012-06-29 06:17:15 UTC ---
Possibly related to bug #14307? I found an issue specifically on x86_64 hosts

If you were running on a x86_64 machine, try compiling your test program with
"-m32" and see if that fixes it

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug network/13904] getaddrinfo does two identical queries, breaks dns round robin with two hosts

[kjp at ci dot uchicago.edu]

http://sourceware.org/bugzilla/show_bug.cgi?id=13904

--- Comment #4 from kjp at ci dot uchicago.edu 2012-06-29 15:10:03 UTC ---
You are the man.  Compiling with 32 changes the behavior - it just sends one
query using send().  64 bit mode does two sendto() calls.

So 32 bit mode has working IP round robin with 2 hosts, 64 bit mode doesn't.


koa@mydev ~$ gcc t.c -m32
koa@mydev ~$ strace -tt -s 100 -e send ./a.out
[ Process PID=14183 runs in 32 bit mode. ]
15:09:32.195930 send(3,
"\307\354\1\0\0\1\0\0\0\0\0\0\7gridftp\10nautilus\4nics\5xsede\3org\0\0\1\0\1",
49, MSG_NOSIGNAL) = 49




koa@mydev ~$ strace -tt -s 100 -e sendto ./a.out
15:09:45.178425 sendto(3, "\24\0\0\0\26\0\1\0039\305\355O\0\0\0\0\0\0\0\0", 20,
0, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 20
15:09:45.182789 sendto(3,
"a]\1\0\0\1\0\0\0\0\0\0\7gridftp\10nautilus\4nics\5xsede\3org\0\0\1\0\1", 49,
MSG_NOSIGNAL, NULL, 0) = 49
15:09:45.183953 sendto(3,
"]\35\1\0\0\1\0\0\0\0\0\0\7gridftp\10nautilus\4nics\5xsede\3org\0\0\1\0\1", 49,
MSG_NOSIGNAL, NULL, 0) = 49

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug network/13904] getaddrinfo does two identical queries, breaks dns round robin with two hosts

[kjp at ci dot uchicago.edu]

http://sourceware.org/bugzilla/show_bug.cgi?id=13904

--- Comment #5 from kjp at ci dot uchicago.edu 2012-06-29 15:13:39 UTC ---
Just to clarify, my second snipped above was with -m64:


koa@mydev ~$ gcc t.c  -m64
koa@mydev ~$ strace -tt -s 100 -e send,sendto ./a.out
15:13:10.946056 sendto(3, "\24\0\0\0\26\0\1\3\6\306\355O\0\0\0\0\0\0\0\0", 20,
0, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 20
15:13:10.950462 sendto(3,
"x\227\1\0\0\1\0\0\0\0\0\0\7gridftp\10nautilus\4nics\5xsede\3org\0\0\1\0\1",
49, MSG_NOSIGNAL, NULL, 0) = 49
15:13:10.951656 sendto(3,
"\244\211\1\0\0\1\0\0\0\0\0\0\7gridftp\10nautilus\4nics\5xsede\3org\0\0\1\0\1",
49, MSG_NOSIGNAL, NULL, 0) = 49

definitely the trigger...

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug network/13904] getaddrinfo does two identical queries, breaks dns round robin with two hosts

[jvb127 at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=13904

Jeroen van Bemmel <jvb127 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |DUPLICATE

--- Comment #6 from Jeroen van Bemmel <jvb127 at gmail dot com> 2012-06-30 15:08:51 UTC ---
Additional test confirms that root cause is the same as #14307. Patch available
for the latter

*** This bug has been marked as a duplicate of bug 14307 ***

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug network/13904] getaddrinfo does two identical queries, breaks dns round robin with two hosts

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=13904

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

-- 
You are receiving this mail because:
You are on the CC list for the bug.