Re: Cyrus-imapd 2.4.17: processes stick on mailbox locking resulting in total mailsystem failure

ellie timoney ellie at fastmail.com
Thu Feb 21 20:20:29 EST 2019 

Hi Ivan,

> #7  0x000056193ed6382e in idle_update ()

> with cyrus-imapd 2.4.17 (cyrus-imapd-2.4.17-13.el7.x86_64 rpm)

It looks like this version is old enough to still be using signal handlers in its IMAP IDLE implementation.  This is known to be a problem, and IDLE was rewritten to not use signals for 2.5 and later.

Thomas Jarosch kindly backported the rewrite for 2.4, and it has been included in releases since 2.4.19 (the current 2.4 release is 2.4.20)

Cheers,

ellie

On Wed, Feb 20, 2019, at 1:15 AM, Ivan Kuznetsov wrote:
> Hello
> 
> I have gdb'ed the locked process, backtrace is below. It seems that 
> problem occurs when imapd process catch a signal when is inside malloc() 
> call. The signal handler has a malloc() call too, so finally there is 
> interlock between two mallocs
> 
> I have only a few time to investigate because locked processes list 
> grows up dramatically. So I didn't found what the signal was. But it 
> seems that there is a bug in imapd code...
> 
> (gdb) thread apply all bt
> 
> Thread 1 (Thread 0x7ff6ead5f840 (LWP 22980)):
> #0  0x00007ff6e83e282c in __lll_lock_wait_private () from /lib64/libc.so.6
> #1  0x00007ff6e835e7e5 in _L_lock_16773 () from /lib64/libc.so.6
> #2  0x00007ff6e835b833 in malloc () from /lib64/libc.so.6
> #3  0x000056193edc9910 in xzmalloc ()
> #4  0x000056193edb2664 in seqset_init ()
> #5  0x000056193ed821b0 in index_tellchanges ()
> #6  0x000056193ed8232b in index_check ()
> #7  0x000056193ed6382e in idle_update ()
> #8  <signal handler called>
> #9  0x00007ff6e83580f0 in _int_malloc () from /lib64/libc.so.6
> #10 0x00007ff6e835b7dc in malloc () from /lib64/libc.so.6
> #11 0x00007ff6e956f4b8 in CRYPTO_malloc () from /lib64/libcrypto.so.10
> #12 0x00007ff6e96397ec in EVP_PKEY_CTX_dup () from /lib64/libcrypto.so.10
> #13 0x00007ff6e962b360 in EVP_MD_CTX_copy_ex () from /lib64/libcrypto.so.10
> #14 0x00007ff6e999ab3d in tls1_mac () from /lib64/libssl.so.10
> #15 0x00007ff6e998db02 in ssl3_read_bytes () from /lib64/libssl.so.10
> #16 0x00007ff6e998a644 in ssl3_read_internal () from /lib64/libssl.so.10
> #17 0x000056193edb9745 in prot_fill ()
> #18 0x000056193eda9ad7 in getword ()
> #19 0x000056193ed670e7 in cmd_idle ()
> #20 0x000056193ed7848d in cmdloop ()
> #21 0x000056193ed79769 in service_main ()
> #22 0x000056193ed62875 in main ()
> 
> 
> 13.12.2018 17:50, Ivan Kuznetsov пишет:
> > Jonk, thank you for the idea. Somewhat looks strange as old mail server 
> > worked w/o this problem 5+ years. But the system environment changed 
> > dramatically, may be some filesystem quircks are significant for this 
> > locks...
> > 
> > I will try gdb'ing the process when problem occurs once more
> > 
> > 13.12.2018 17:34, John Wade пишет:
> >> Without running gdb on the process, I have no idea, but your problem 
> >> sounds similar to something we hit a very long time ago:
> >>
> >> See https://www.oakton.edu/user/3/jwade/cyrus/Readme.html
> >>
> >> In our cases, the problem was the imapd process that was holding the 
> >> lock was trying to obtain a second lock on the same file.   What does 
> >> a stack trace look like on the imapd process that is holding the lock? 
> >> It would appear the lock process has changed since I last looked at 
> >> this, so this may not be a help at all.
> >>
> >> Good luck,
> >> John
> >>
> >>
> >>
> >> On 12/13/2018 5:21 AM, Ivan Kuznetsov wrote:
> >>> Hello
> >>>
> >>> We had a company mail server under Oracle Linux 6 (a clone of RHEL6) 
> >>> with cyrus-imapd 2.3.16 working for years w/o problems. There are >9M 
> >>> messages in ~9500 mailboxes in two partitions. Daily mail traffic is 
> >>> 20-50K messages.
> >>>
> >>> Some weeks ago we migrated the server to a new one under Oracle Linux 
> >>> 7 with cyrus-imapd 2.4.17 (cyrus-imapd-2.4.17-13.el7.x86_64 rpm) and 
> >>> now have problem. Some times a week one of imapd processes locks an 
> >>> "INBOX" mailbox with corresponding 
> >>> /var/lib/imap/lock/user/<user>.lock file and does not unlock it 
> >>> anymore. Other imapd processes trying to access this mailbox sticks 
> >>> waiting to obtain the lock. The bigger problem is that lmtpd 
> >>> processes trying to deliver new mail to this mailbox hangs too. The 
> >>> number of lmtpd processes is limited (maxchild=32) to limit the 
> >>> server load, so free lmtpd pool become empty after a time, and mail 
> >>> delivery stopsto all the mailboxes. MTA (postfix) mail queue blows up 
> >>> quickly
> >>>
> >>> Example lsof output:
> >>>
> >>> lmtpd   8182 cyrus   18uR  REG              249,0         0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   8183 cyrus   18uR  REG              249,0         0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   8187 cyrus   18uR  REG              249,0         0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   8771 cyrus   18uR  REG              249,0         0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   8834 cyrus   18uR  REG              249,0         0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   9123 cyrus   18uR  REG              249,0         0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   9631 cyrus   18uR  REG              249,0         0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   10343 cyrus   18uR  REG              249,0         0 
> >>> 202944402 /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   10437 cyrus   18uR  REG              249,0         0 
> >>> 202944402 /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   11411 cyrus   18uR  REG              249,0         0 
> >>> 202944402 /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   11413 cyrus   18uR  REG              249,0         0 
> >>> 202944402 /var/lib/imap/lock/user/smilovsky.lock
> >>> lmtpd   11506 cyrus   18uR  REG              249,0         0 
> >>> 202944402 /var/lib/imap/lock/user/smilovsky.lock
> >>>
> >>> [root at hippo4 bin]# lsof /var/lib/imap/lock/user/smilovsky.lock | grep 
> >>> '^imapd'
> >>> imapd    9132 cyrus   19uR  REG  249,0        0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> imapd    9154 cyrus   19uR  REG  249,0        0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> imapd   10311 cyrus   19uR  REG  249,0        0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> imapd   10746 cyrus   19uR  REG  249,0        0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> imapd   11843 cyrus   19uR  REG  249,0        0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> imapd   12059 cyrus   19uR  REG  249,0        0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>> imapd   21885 cyrus   19uR  REG  249,0        0 202944402 
> >>> /var/lib/imap/lock/user/smilovsky.lock
> >>>
> >>> In this case the root cause imapd process is 21885. strace shows that 
> >>> the process waits on a futex forever:
> >>>
> >>> [root at hippo4 bin]# strace -tt -f -p 21885
> >>> strace: Process 21885 attached
> >>> 13:07:28.264713 futex(0x7f6dcc5ac760, FUTEX_WAIT_PRIVATE, 2, 
> >>> NULL^Cstrace: Process 21885 detached
> >>>  <detached ...>
> >>>
> >>> Killing the process frees the lock, all the other stuck processes 
> >>> runs and the problem disappears in a few seconds.
> >>>
> >>> Investigation shows that this process has a long-term connection from 
> >>> a user MUA (Thunderbird) and deletes mail messages time-to-time. This 
> >>> may be a Thunderbird 'filter' thread
> >>>
> >>> [root at hippo4 bin]# grep 'imap\[21885\]' /var/log/maillog
> >>> [...]
> >>> Dec 13 09:59:11 hippo4 imap[21885]: starttls: TLSv1.2 with cipher 
> >>> DHE-RSA-AES256-SHA (256/256 bits new) no authentication
> >>> Dec 13 09:59:11 hippo4 imap[21885]: login: thunder.solvo.ru 
> >>> [172.16.85.69] smilovsky CRAM-MD5+TLS User logged in 
> >>> SESSIONID=<hippo.solvo.ru-21885-1544684350-1>
> >>> Dec 13 09:59:11 hippo4 imap[21885]: client id: "name" "Thunderbird" 
> >>> "version" "52.5.2"
> >>> Dec 13 09:59:11 hippo4 imap[21885]: Expunged 1 messages from 
> >>> user.smilovsky
> >>> Dec 13 09:59:12 hippo4 imap[21885]: Expunged 1 messages from 
> >>> user.smilovsky
> >>> Dec 13 09:59:12 hippo4 imap[21885]: Expunged 1 messages from 
> >>> user.smilovsky
> >>> Dec 13 09:59:12 hippo4 imap[21885]: Expunged 1 messages from 
> >>> user.smilovsky
> >>> Dec 13 10:01:45 hippo4 imap[21885]: Expunged 1 messages from 
> >>> user.smilovsky
> >>> Dec 13 10:01:53 hippo4 imap[21885]: Expunged 1 messages from 
> >>> user.smilovsky
> >>> Dec 13 10:03:17 hippo4 imap[21885]: Expunged 1 messages from 
> >>> user.smilovsky
> >>> Dec 13 10:09:06 hippo4 imap[21885]: Expunged 1 messages from 
> >>> user.smilovsky
> >>> Dec 13 10:09:19 hippo4 imap[21885]: Expunged 1 messages from 
> >>> user.smilovsky
> >>>
> >>> Problem is sporadic, I didn't see any correlation with server load, 
> >>> time of day, user name and so on
> >>>
> >>> Removing "maxchild=" parameter for lmtp just delay the final as the 
> >>> server system resources are limited. Now I wrote a patrol script 
> >>> counting locks and killing imapd if locks number is growing up. The 
> >>> trouble is I can't reliably determine the root cause imapd and kill 
> >>> them one-by-one
> >>>
> >>> Any ideas more?
> >>>
> >>> Ivan Kuznetsov, SOLVO ltd
> >>> ----
> >>> Cyrus Home Page: http://www.cyrusimap.org/
> >>> List Archives/Info: http://lists.andrew.cmu.edu/pipermail/info-cyrus/
> >>> To Unsubscribe:
> >>> https://lists.andrew.cmu.edu/mailman/listinfo/info-cyrus
> >>
> > 
> 
> -- 
> С уважением, Иван Кузнецов
> Руководитель технического отдела
> 
> Компания "СОЛВО"
> +7(812)60-60-555
> +7(495)66-83-003
> +7(921)740-72-61
> http://www.solvo.ru
> ----
> Cyrus Home Page: http://www.cyrusimap.org/
> List Archives/Info: http://lists.andrew.cmu.edu/pipermail/info-cyrus/
> To Unsubscribe:
> https://lists.andrew.cmu.edu/mailman/listinfo/info-cyrus

More information about the Info-cyrus mailing list