The system hang, linux from scratch. I have changed the live kernel from linux-2.6.35.4 to linux-2.6.32.61 , to see if the fault still occurs. The kernel 2.6.35.4 was working fine with all version up to dovecot 2.1.12 , from which i made update to 2.1.17.

dovecot -n # 2.1.17: /usr/dovecot21/etc/dovecot/dovecot.conf # OS: Linux 2.6.32.61 i686 auth_cache_negative_ttl = 1 secs auth_cache_size = 2 M auth_failure_delay = 4 secs auth_mechanisms = plain login digest-md5 cram-md5 auth_worker_max_count = 100 base_dir = /var/run/dovecot/ default_client_limit = 4096 default_internal_user = vmail default_login_user = nobody default_process_limit = 256 deliver_log_format = mail delivery from=%f subject=%s msgid=%m: %$ dict { acl = mysql:/usr/dovecot21/etc/dovecot/dovecot-dict-sql.conf.ext } disable_plaintext_auth = no first_valid_uid = 1 lda_mailbox_autocreate = yes lda_mailbox_autosubscribe = yes listen = * mail_location = maildir:~/Maildir mail_plugins = " quota acl trash notify mail_log" managesieve_notify_capability = mailto managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date ihave namespace { hidden = no list = children location = maildir:%%h/Maildir:INDEX=~/Maildir/shared/%%u prefix = shared/%%u/ separator = / subscriptions = no type = shared } namespace inbox { inbox = yes list = yes location = mailbox Drafts { special_use = \Drafts } mailbox Junk { special_use = \Junk } mailbox Sent { special_use = \Sent } mailbox "Sent Messages" { special_use = \Sent } mailbox Trash { special_use = \Trash } prefix = separator = / subscriptions = yes type = private } passdb { args = /usr/dovecot21/etc/dovecot/dovecot-sql.conf.ext driver = sql } plugin { acl = vfile acl_defaults_from_inbox = yes acl_shared_dict = proxy::acl autocreate = Trash autocreate2 = Drafts autocreate3 = Sent autosubscribe = Trash autosubscribe2 = Drafts autosubscribe3 = INBOX autosubscribe4 = Sent mail_log_events = delete mailbox_delete mailbox_rename mail_log_fields = box subject from msgid size quota = maildir:User quota quota_warning = storage=95%% quota-warning 95 %u quota_warning2 = storage=95%% quota-warning 90 %u quota_warning3 = storage=85%% quota-warning 85 %u sieve = ~/.dovecot.sieve sieve_dir = ~/sieve sieve_max_redirects = 10 trash = /usr/dovecot21/etc/dovecot/dovecot-trash.conf.ext } postmaster_address = postmaster@dacris.net protocols = imap quota_full_tempfail = yes rejection_subject = Rejected: %s: %r service auth { unix_listener auth-client { mode = 0666 user = vmail } unix_listener auth-userdb { mode = 0666 user = vmail } } service dict { unix_listener dict { user = vmail } } service imap-login { process_min_avail = 4 } service imap-postlogin { executable = script-login /bin/imap.sh unix_listener imap-postlogin { mode = 01232 } } service imap { executable = imap imap-postlogin process_limit = 1024 vsz_limit = 1 G } service quota-warning { executable = script /bin/quota_warning.sh unix_listener quota-warning { user = vmail } user = vmail } ssl_cert = </etc/ssl/certs/dovecot.pem ssl_key = </etc/ssl/private/dovecot.pem userdb { args = /usr/dovecot21/etc/dovecot/dovecot-sql.conf.ext driver = sql } protocol lda { mail_plugins = " quota acl trash notify mail_log sieve autocreate" } protocol imap { imap_client_workarounds = delay-newmail mail_max_userip_connections = 20 mail_plugins = " quota acl trash notify mail_log imap_quota imap_acl" }

Log from kernel: Jul 11 10:14:01 mail kernel: BUG: Bad page map in process imap-login
pte:c926b025 pmd:4597c067 Jul 11 10:14:01 mail kernel: page:c2f2ed60 count:1 mapcount:-1 mapping:ec5a03a0 index:0x4ab Jul 11 10:14:01 mail kernel: page flags: 0x80020068(uptodate|lru|active|mappedtodisk) Jul 11 10:14:01 mail kernel: addr:b73f4000 vm_flags:08000075 anon_vma:(null) mapping:e289ec88 index:7b Jul 11 10:14:01 mail kernel: vma->vm_ops->fault: filemap_fault+0x0/0x2fa Jul 11 10:14:01 mail kernel: vma->vm_file->f_op->mmap: ext4_file_mmap+0x0/0x39 Jul 11 10:14:01 mail kernel: Pid: 22889, comm: imap-login Not tainted 2.6.35.4 #2 Jul 11 10:14:01 mail kernel: Call Trace: Jul 11 10:14:01 mail kernel: [<c1078901>] ? print_bad_pte+0x13a/0x14b Jul 11 10:14:01 mail kernel: [<c107b206>] ? unmap_vmas+0x33b/0x62d Jul 11 10:14:01 mail kernel: [<c10272cc>] ? try_to_wake_up+0x206/0x210 Jul 11 10:14:01 mail kernel: [<c107ccc7>] ? exit_mmap+0x8c/0x107 Jul 11 10:14:01 mail kernel: [<c102976f>] ? mmput+0x1c/0x8c Jul 11 10:14:01 mail kernel: [<c102c850>] ? exit_mm+0xdc/0xe4 Jul 11 10:14:01 mail kernel: [<c103da3c>] ? hrtimer_try_to_cancel+0x55/0x5b Jul 11 10:14:01 mail kernel: [<c104dd0d>] ? acct_collect+0x77/0x126 Jul 11 10:14:01 mail kernel: [<c102dccb>] ? do_exit+0x1c8/0x5bc Jul 11 10:14:01 mail kernel: [<c109fd4d>] ? mntput_no_expire+0x15/0xad Jul 11 10:14:01 mail kernel: [<c102e119>] ? do_group_exit+0x5a/0x7d Jul 11 10:14:01 mail kernel: [<c102e14d>] ? sys_exit_group+0x11/0x14 Jul 11 10:14:01 mail kernel: [<c100254c>] ? sysenter_do_call+0x12/0x22 Jul 11 10:14:01 mail kernel: Disabling lock debugging due to kernel taint Jul 11 10:14:01 mail kernel: BUG: Bad page state in process imap-login
pfn:c926b Jul 11 10:14:01 mail kernel: page:c2f2ed60 count:0 mapcount:-1 mapping:ec5a03a0 index:0x4ab Jul 11 10:14:01 mail kernel: page flags: 0x80020008(uptodate|mappedtodisk) Jul 11 10:14:01 mail kernel: Pid: 22889, comm: imap-login Tainted: G
B 2.6.35.4 #2 Jul 11 10:14:01 mail kernel: Call Trace: Jul 11 10:14:01 mail kernel: [<c106c916>] ? bad_page+0x9c/0xae Jul 11 10:14:01 mail kernel: [<c106d4dc>] ? free_pages_prepare+0x55/0xc5 Jul 11 10:14:01 mail kernel: [<c106d5f0>] ? free_hot_cold_page+0x20/0xef Jul 11 10:14:01 mail kernel: [<c106d739>] ? __pagevec_free+0x1a/0x21 Jul 11 10:14:01 mail kernel: [<c106fb3a>] ? release_pages+0x165/0x16d Jul 11 10:14:01 mail kernel: [<c1083302>] ? free_pages_and_swap_cache+0x68/0x74 Jul 11 10:14:01 mail kernel: [<c107b251>] ? unmap_vmas+0x386/0x62d Jul 11 10:14:01 mail kernel: [<c10272cc>] ? try_to_wake_up+0x206/0x210 Jul 11 10:14:01 mail kernel: [<c107ccc7>] ? exit_mmap+0x8c/0x107 Jul 11 10:14:01 mail kernel: [<c102976f>] ? mmput+0x1c/0x8c Jul 11 10:14:01 mail kernel: [<c102c850>] ? exit_mm+0xdc/0xe4 Jul 11 10:14:01 mail kernel: [<c103da3c>] ? hrtimer_try_to_cancel+0x55/0x5b Jul 11 10:14:01 mail kernel: [<c104dd0d>] ? acct_collect+0x77/0x126 Jul 11 10:14:01 mail kernel: [<c102dccb>] ? do_exit+0x1c8/0x5bc Jul 11 10:14:01 mail kernel: [<c109fd4d>] ? mntput_no_expire+0x15/0xad Jul 11 10:14:01 mail kernel: [<c102e119>] ? do_group_exit+0x5a/0x7d Jul 11 10:14:01 mail kernel: [<c102e14d>] ? sys_exit_group+0x11/0x14 Jul 11 10:14:01 mail kernel: [<c100254c>] ? sysenter_do_call+0x12/0x22