When we upgrade our kernels from 2.6.32.2 to 3.2.16 something strange has happened. On high traffic dovecot/auth looks like not responding.

We found a lot of this lines at the log: dovecot: pop3-login: Error: net_connect_unix(pop3) failed: Resource temporarily unavailable (...) and clients stop authorizing

Some other errors follow in the wake of: dovecot: pop3: Error: Raw backtrace: /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x373ca) [0x7768a3ca] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x3743b) [0x7768a43b] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(i_fatal+0) [0x7766048b] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x4593a) [0x7769893a] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(io_add+0xaf) [0x7769757f] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(master_service_init_finish+0x19a) [0x77683c2a] -> dovecot/pop3(main+0xfc) [0x804a90c] -> /lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xf3) [0x774c04d3] -> dovecot/pop3() [0x804aba9] dovecot: pop3: Error: Raw backtrace: /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x373ca) [0x7768a3ca] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x3743b) [0x7768a43b] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(i_fatal+0) [0x7766048b] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x4593a) [0x7769893a] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(io_add+0xaf) [0x7769757f] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(master_service_init_finish+0x19a) [0x77683c2a] -> dovecot/pop3(main+0xfc) [0x804a90c] -> /lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xf3) [0x774c04d3] -> dovecot/pop3() [0x804aba9] dovecot: master: Error: service(pop3): child 18756 killed with signal 6 (core dumped) dovecot: master: Error: service(pop3): child 18756 killed with signal 6 (core dumped) dovecot: master: Error: service(pop3): command startup failed, throttling dovecot: master: Error: service(pop3): command startup failed, throttling dovecot: pop3-login: Error: Raw backtrace: /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x373ca) [0x776b73ca] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x3743b) [0x776b743b] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(i_fatal+0) [0x7768d48b] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x4593a) [0x776c593a] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(io_add+0xaf) [0x776c457f] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(master_service_init_finish+0x19a) [0x776b0c2a] -> /opt/dovecot2/lib/dovecot/libdovecot-login.so.0(main+0x143) [0x77705383] -> /lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xf3) [0x774ed4d3] -> dovecot/pop3-login() [0x8049471] dovecot: pop3-login: Error: Raw backtrace: /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x373ca) [0x776fd3ca] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x3743b) [0x776fd43b] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(i_fatal+0) [0x776d348b] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x4593a) [0x7770b93a] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(io_add+0xaf) [0x7770a57f] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(master_service_init_finish+0x19a) [0x776f6c2a] -> /opt/dovecot2/lib/dovecot/libdovecot-login.so.0(main+0x143) [0x7774b383] -> /lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xf3) [0x775334d3] -> dovecot/pop3-login() [0x8049471]

And example stack trace (from pop3, pop3-login throws almost the same): #0 0x776f6424 in __kernel_vsyscall () No symbol table info available. #1 0x7744d1ef in __GI_raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64 resultvar = <optimized out> resultvar = <optimized out> pid = 2002518004 selftid = 25476 #2 0x77450835 in __GI_abort () at abort.c:91 save_stage = 2 act = {__sigaction_handler = {sa_handler = 0x9bce4a8, sa_sigaction = 0x9bce4a8}, sa_mask = {__val = {163409408, 2002781570, 163374248, 603, 163374280, 604, 163374280, 2001703379, 0, 2002790760, 2140717252, 163374280, 0, 2003786736, 2002596704, 0, 2002618953, 2003087348, 2140717196, 0, 163409408, 2001286473, 163374248, 10, 2000834616, 2002534400, 604, 2003087348, 604, 2002791863, 4294967295, 10}}, sa_flags = 2140717316, sa_restorer = 0x7764bd84 <pid.3786>} sigs = {__val = {32, 0 <repeats 31 times>}} #3 0x77603390 in default_fatal_finish (type=<optimized out>, status=<optimized out>) at failures.c:187 backtrace = 0x9bce098 "/opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x3837a) [0x7760337a] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(+0x383eb) [0x776033eb] -> /opt/dovecot2/lib/dovecot/libdovecot.so.0(i_fatal+0) [0x775d877a"... #4 0x776033eb in i_internal_fatal_handler (ctx=0x7f98c174, format=0x9bd6db0 "(25476) epoll_ctl(%s, %d) failed: %m", args=0x7f98c194 "\\\323bw\006") at failures.c:688 status = 0 #5 0x775d877a in i_panic (format=0x7762d364 "epoll_ctl(%s, %d) failed: %m") at failures.c:263 ctx = {type = LOG_TYPE_PANIC, exit_status = 0, timestamp = 0x0} args = 0x7f98c194 "\\\323bw\006" f = <optimized out> #6 0x77611d8a in io_loop_handle_add (io=0x9bd6d78) at ioloop-epoll.c:119 ---Type <return> to continue, or q <return> to quit--- ctx = 0x9bd64d8 list = <optimized out> event = {events = 24, data = {ptr = 0x9bd6da0, fd = 163409312, u32 = 163409312, u64 = 163409312}} op = 1 first = true #7 0x776109af in io_add (fd=6, condition=IO_ERROR, callback=0x775fd030 <master_status_error>, context=0x9bd6300) at ioloop.c:54 io = <optimized out> __FUNCTION__ = "io_add" #8 0x775fca9a in master_service_init_finish (service=0x9bd6300) at master-service.c:381 sigint_flags = <optimized out> st = {st_dev = 8, __pad1 = 0, __st_ino = 1286567453, st_mode = 4480, st_nlink = 1, st_uid = 0, st_gid = 0, st_rdev = 0, __pad2 = 0, st_size = 0, st_blksize = 4096, st_blocks = 0, st_atim = {tv_sec = 1338389522, tv_nsec = 269436805}, st_mtim = {tv_sec = 1338389522, tv_nsec = 269436805}, st_ctim = { tv_sec = 1338389522, tv_nsec = 269436805}, st_ino = 1286567453} value = <optimized out> count = 1 __FUNCTION__ = "master_service_init_finish" #9 0x0804a954 in main (argc=1, argv=0x7f98c414) at main.c:232 set_roots = {0x804ee40, 0x0} service_flags = <optimized out> storage_service_flags = MAIL_STORAGE_SERVICE_FLAG_DISALLOW_ROOT postlogin_socket_path = 0x0 username = 0x0 c = <optimized out>

We do some investigation. Restart helped for a moment, but problem was returning. When we back to older kernel - everything back to normal.

We compile Dovecot with poll instead of epoll (--with-ioloop=poll) and this works for us.

Is any problem with epoll on 3.2.x kernels? Or maybe this is Dovecot problem? Maybe this is not connected with epoll, but epoll is interferes with this.

Problem on Dovecot 2.0.11 and 2.0.20.

-- Len7hir