#3266 Deadlock in watchdog's signal handler
Closed: Fixed None Opened 3 years ago by fidencio.

sssd_be deadlocks due to the use of non async-signal-safe functions from the watchdog signal handler.

  [root@dusan ~]# pstack 17922
    #0  __lll_lock_wait_private () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:95
    #1  0x00007fe707d04f93 in _L_lock_14932 () from /lib64/libc.so.6
    #2  0x00007fe707d02013 in __GI___libc_malloc (bytes=140630248638304, bytes@entry=15) at malloc.c:2891
    #3  0x00007fe707d0888a in __GI___strdup (s=0x7fe707dff4f7 "/etc/localtime") at strdup.c:42
    #4  0x00007fe707d31b61 in tzset_internal (always=<optimized out>, explicit=explicit@entry=1) at tzset.c:438
    #5  0x00007fe707d32523 in __tz_convert (timer=timer@entry=0x7ffcd5d2b090, use_localtime=use_localtime@entry=1, tp=tp@entry=0x7fe708041d40 <_tmbuf>) at tzset.c:621
    #6  0x00007fe707d30521 in __GI_localtime (t=t@entry=0x7ffcd5d2b090) at localtime.c:42
    #7  0x00007fe70886c7b0 in sss_vdebug_fn (file=<optimized out>, line=<optimized out>, function=0x7fe70bff27f0 <__FUNCTION__.9379> "watchdog_handler", level=16, flags=flags@entry=0, format=format@entry=0x7fe70bff2760 "Watchdog timer overflow, killing process!\n", ap=ap@entry=0x7ffcd5d2b130) at src/util/debug.c:248
    #8  0x00007fe70886c995 in sss_debug_fn (file=file@entry=0x7fe70bff263b "src/util/util_watchdog.c", line=line@entry=82, function=function@entry=0x7fe70bff27f0 <__FUNCTION__.9379> "watchdog_handler", level=level@entry=16, format=format@entry=0x7fe70bff2760 "Watchdog timer overflow, killing process!\n") at src/util/debug.c:284
    #9  0x00007fe70bfdb409 in watchdog_handler (sig=<optimized out>) at src/util/util_watchdog.c:81
    #10 <signal handler called>
    #11 0x00007fe707cff664 in _int_malloc (av=av@entry=0x7fe70803c760 <main_arena>, bytes=bytes@entry=151) at malloc.c:3494
    #12 0x00007fe707d01fbc in __GI___libc_malloc (bytes=bytes@entry=151) at malloc.c:2893
    #13 0x00007fe708450749 in __talloc_with_prefix (prefix_len=0, size=55, context=0x7fe718373210) at ../talloc.c:668
    #14 __talloc (size=55, context=0x7fe718373210) at ../talloc.c:708
    #15 _talloc_named_const (name=0x7fe70bb7015d "../common/ldb_pack.c:425", size=55, context=0x7fe718373210) at ../talloc.c:865
    #16 talloc_named_const (context=<optimized out>, size=size@entry=55, name=name@entry=0x7fe70bb7015d "../common/ldb_pack.c:425") at ../talloc.c:1606
    #17 0x00007fe70bb61803 in ldb_unpack_data_only_attr_list (ldb=ldb@entry=0x7fe70e4d52c0, data=data@entry=0x7ffcd5d2b990, message=0x7fe7184aa1e0, list=list@entry=0x0, list_size=list_size@entry=0, nb_elements_in_db=nb_elements_in_db@entry=0x0) at ../common/ldb_pack.c:425
    #18 0x00007fe70bb61a7d in ldb_unpack_data (ldb=ldb@entry=0x7fe70e4d52c0, data=data@entry=0x7ffcd5d2b990, message=<optimized out>) at ../common/ldb_pack.c:470
    #19 0x00007fe6fdc29b46 in ltdb_parse_data_unpack (key=..., data=..., private_data=0x7ffcd5d2ba70) at ../ldb_tdb/ldb_search.c:249
    #20 0x00007fe70a5e0a24 in tdb_parse_data (tdb=tdb@entry=0x7fe70e4eaa10, key=..., offset=15619748, len=414772, parser=parser@entry=0x7fe6fdc29b10 <ltdb_parse_data_unpack>, private_data=private_data@entry=0x7ffcd5d2ba70) at ../common/io.c:637
    #21 0x00007fe70a5dc1fc in tdb_parse_record (tdb=0x7fe70e4eaa10, key=..., parser=parser@entry=0x7fe6fdc29b10 <ltdb_parse_data_unpack>, private_data=private_data@entry=0x7ffcd5d2ba70) at ../common/tdb.c:253
    #22 0x00007fe6fdc29e7b in ltdb_search_dn1 (module=module@entry=0x7fe70e4eab50, dn=dn@entry=0x7fe7183c4940, msg=msg@entry=0x7fe7184aa1e0) at ../ldb_tdb/ldb_search.c:287
    #23 0x00007fe6fdc2acbb in ltdb_dn_list_load (module=module@entry=0x7fe70e4eab50, dn=dn@entry=0x7fe7183c4940, list=list@entry=0x7fe7183c3a30) at ../ldb_tdb/ldb_index.c:181
    #24 0x00007fe6fdc2bbbb in ltdb_index_add1 (module=module@entry=0x7fe70e4eab50, dn=dn@entry=0x7fe7183bf3e0 "name=testuser7045@domain.com,cn=users,cn=DOMAIN.COM,cn=sysdb", v_idx=v_idx@entry=0, el=<optimized out>, el=<optimized out>) at ../ldb_tdb/ldb_index.c:1134
    #25 0x00007fe6fdc2c62c in ltdb_index_add_el (el=0x7fe7184aa3e0, dn=0x7fe7183bf3e0 "name=testuser7045@domain.com,cn=users,cn=DOMAIN.COM,cn=sysdb", module=0x7fe70e4eab50) at ../ldb_tdb/ldb_index.c:1180
    #26 ltdb_index_add_element (module=module@entry=0x7fe70e4eab50, dn=<optimized out>, el=el@entry=0x7fe7184aa3e0) at ../ldb_tdb/ldb_index.c:1290
    #27 0x00007fe6fdc290bb in ltdb_modify_internal (module=module@entry=0x7fe70e4eab50, msg=0x7fe7183bf0c0, req=req@entry=0x7fe7183bdc10) at ../ldb_tdb/ldb_tdb.c:903
    #28 0x00007fe6fdc2958a in ltdb_modify (ctx=0x7fe7183c2950, ctx=0x7fe7183c2950) at ../ldb_tdb/ldb_tdb.c:998
    #29 ltdb_callback (ev=<optimized out>, te=<optimized out>, t=..., private_data=<optimized out>) at ../ldb_tdb/ldb_tdb.c:1380
    #30 0x00007fe708664b4f in tevent_common_loop_timer_delay (ev=ev@entry=0x7fe70e4d2890) at ../tevent_timed.c:341
    #31 0x00007fe708665b5a in epoll_event_loop_once (ev=0x7fe70e4d2890, location=<optimized out>) at ../tevent_epoll.c:911
    #32 0x00007fe708664257 in std_event_loop_once (ev=0x7fe70e4d2890, location=0x7fe70bb72ec5 "../common/ldb.c:631") at ../tevent_standard.c:114
    #33 0x00007fe70866040d in _tevent_loop_once (ev=ev@entry=0x7fe70e4d2890, location=location@entry=0x7fe70bb72ec5 "../common/ldb.c:631") at ../tevent.c:533
    #34 0x00007fe70bb6bc4f in ldb_wait (handle=0x7fe7183c4530, type=<optimized out>) at ../common/ldb.c:631
    #35 0x00007fe70bb6c793 in ldb_autotransaction_request (ldb=0x7fe70e4d52c0, req=0x7fe7183bdc10) at ../common/ldb.c:573
    #36 0x00007fe70bb6d263 in ldb_modify (ldb=ldb@entry=0x7fe70e4d52c0, message=<optimized out>) at ../common/ldb.c:1655
    #37 0x00007fe70bfa2ab5 in sysdb_set_cache_entry_attr (ldb=0x7fe70e4d52c0, entry_dn=entry_dn@entry=0x7fe7183c4760, attrs=attrs@entry=0x7fe7183bf680, mod_op=mod_op@entry=2) at src/db/sysdb_ops.c:1159
    #38 0x00007fe70bfa304d in sysdb_rep_ts_entry_attr (sysdb=0x7fe70e4eadd0, attrs=0x7fe7183bf680, entry_dn=0x7fe7183c4760) at src/db/sysdb_ops.c:1218
    #39 sysdb_set_ts_entry_attr (sysdb=sysdb@entry=0x7fe70e4eadd0, entry_dn=entry_dn@entry=0x7fe7183c4760, attrs=attrs@entry=0x7fe7183bb840, mod_op=mod_op@entry=2) at src/db/sysdb_ops.c:1248
    #40 0x00007fe70bfa4aa9 in sysdb_set_entry_attr (sysdb=0x7fe70e4eadd0, entry_dn=0x7fe7183c4760, attrs=attrs@entry=0x7fe7183bb840, mod_op=mod_op@entry=2) at src/db/sysdb_ops.c:1199
    #41 0x00007fe70bfa4b5f in sysdb_set_user_attr (domain=domain@entry=0x7fe70e4d62f0, name=name@entry=0x7fe7183c01f0 "testuser7045@domain.com", attrs=attrs@entry=0x7fe7183bb840, mod_op=mod_op@entry=2) at src/db/sysdb_ops.c:1285
    #42 0x00007fe70bfa58c3 in sysdb_add_user (domain=domain@entry=0x7fe70e4d62f0, name=name@entry=0x7fe7183c01f0 "testuser7045@domain.com", uid=uid@entry=1415408147, gid=<optimized out>, gid@entry=1415400513, gecos=gecos@entry=0x7fe710465d00 "Test User7045", homedir=homedir@entry=0x0, shell=shell@entry=0x0, orig_dn=orig_dn@entry=0x7fe710465940 "CN=Test User7045,OU=Sales,DC=DOMAIN,DC=COM", attrs=attrs@entry=0x7fe7183bb840, cache_timeout=cache_timeout@entry=5400, now=now@entry=1481105315) at src/db/sysdb_ops.c:1928
    #43 0x00007fe70bfab271 in sysdb_store_new_user (now=1481105315, cache_timeout=5400, attrs=0x7fe7183bb840, orig_dn=0x7fe710465940 "CN=Test User7045,OU=Sales,DC=DOMAIN,DC=COM", shell=0x0, homedir=0x0, gecos=0x7fe710465d00 "Test User7045", gid=1415400513, uid=1415408147, name=0x7fe7183c01f0 "testuser7045@domain.com", domain=0x7fe70e4d62f0) at src/db/sysdb_ops.c:2549
    #44 sysdb_store_user (domain=domain@entry=0x7fe70e4d62f0, name=0x7fe7183c01f0 "testuser7045@domain.com", pwd=pwd@entry=0x0, uid=1415408147, gid=1415400513, gecos=gecos@entry=0x7fe710465d00 "Test User7045", homedir=homedir@entry=0x0, shell=shell@entry=0x0, orig_dn=orig_dn@entry=0x7fe710465940 "CN=Test User7045,OU=Sales,DC=DOMAIN,DC=COM", attrs=attrs@entry=0x7fe7183bb840, remove_attrs=0x7fe7183c08a0, cache_timeout=cache_timeout@entry=5400, now=now@entry=1481105315) at src/db/sysdb_ops.c:2499
    #45 0x00007fe6fba0d9f9 in sdap_save_user (memctx=memctx@entry=0x7fe70e544ee0, opts=opts@entry=0x7fe70e518400, dom=dom@entry=0x7fe70e4d62f0, attrs=<optimized out>, _usn_value=_usn_value@entry=0x7ffcd5d2c260, now=now@entry=1481105315) at src/providers/ldap/sdap_async_users.c:509
    #46 0x00007fe6fba0df9a in sdap_save_users (memctx=memctx@entry=0x7fe70e544e40, sysdb=0x7fe70e4eadd0, dom=0x7fe70e4d62f0, opts=0x7fe70e518400, users=<optimized out>, num_users=10006, _usn_value=_usn_value@entry=0x7fe70e544e60) at src/providers/ldap/sdap_async_users.c:572
    #47 0x00007fe6fba0e460 in sdap_get_users_done (subreq=<optimized out>) at src/providers/ldap/sdap_async_users.c:938
    #48 0x00007fe6fba0c9d5 in sdap_search_user_process (subreq=0x0) at src/providers/ldap/sdap_async_users.c:814
    #49 0x00007fe6fba07379 in generic_ext_search_handler (subreq=0x0, opts=<optimized out>) at src/providers/ldap/sdap_async.c:1689
    #50 0x00007fe6fba0991b in sdap_get_generic_op_finished (op=<optimized out>, reply=<optimized out>, error=<optimized out>, pvt=<optimized out>) at src/providers/ldap/sdap_async.c:1621
    #51 0x00007fe6fba083cd in sdap_process_message (ev=<optimized out>, sh=<optimized out>, msg=0x7fe70e5f9ce0) at src/providers/ldap/sdap_async.c:353
    #52 sdap_process_result (ev=<optimized out>, pvt=<optimized out>) at src/providers/ldap/sdap_async.c:197
    #53 0x00007fe708664b4f in tevent_common_loop_timer_delay (ev=ev@entry=0x7fe70e4cbc30) at ../tevent_timed.c:341
    #54 0x00007fe708665b5a in epoll_event_loop_once (ev=0x7fe70e4cbc30, location=<optimized out>) at ../tevent_epoll.c:911
    #55 0x00007fe708664257 in std_event_loop_once (ev=0x7fe70e4cbc30, location=0x7fe70bfee8e7 "src/util/server.c:702") at ../tevent_standard.c:114
    #56 0x00007fe70866040d in _tevent_loop_once (ev=ev@entry=0x7fe70e4cbc30, location=location@entry=0x7fe70bfee8e7 "src/util/server.c:702") at ../tevent.c:533
    #57 0x00007fe7086605ab in tevent_common_loop_wait (ev=0x7fe70e4cbc30, location=0x7fe70bfee8e7 "src/util/server.c:702") at ../tevent.c:637
    #58 0x00007fe7086641f7 in std_event_loop_wait (ev=0x7fe70e4cbc30, location=0x7fe70bfee8e7 "src/util/server.c:702") at ../tevent_standard.c:140
    #59 0x00007fe70bfd1993 in server_loop (main_ctx=0x7fe70e4cd080) at src/util/server.c:702
    #60 0x00007fe70c84cb82 in main (argc=8, argv=<optimized out>) at src/providers/data_provider_be.c:587

Patch submitted: https://github.com/SSSD/sssd/pull/107

owner: somebody => fidencio
patch: 0 => 1

Fields changed

milestone: NEEDS_TRIAGE => SSSD 1.14.3

master:

sssd-1-14:

resolution: => fixed
status: new => closed

Metadata Update from @fidencio:
- Issue assigned to fidencio
- Issue set to the milestone: SSSD 1.14.3

3 years ago

Hi, my understanding is that this issue should be fixed for RHEL 7.3 in...

https://access.redhat.com/errata/RHBA-2017:0908

... however the updated packages don't appear to fix the problem.

With enumeration enabled, sssd_be sits at 100% and is continually restarted.

but that's a different problem, right? The issue was not about restarting sssd_be, but about /not being able/ to restart sssd_be because when the watchdog fired, the debug message used in the watchdog's signal handler used an unsafe function which deadlocked the sssd_be process about to be restarted.

If a large domain is being enumerated and the enumeration takes longer than the default timeout, sssd_be will be restarted. Either don't use enumeration (that's the preferred setup anyway) or increase the timeout..

Metadata Update from @jhrozek:
- Custom field design_review reset (from 0)
- Custom field mark reset (from 0)
- Custom field patch adjusted to on (was: 1)
- Custom field review reset (from 0)
- Custom field sensitive reset (from 0)
- Custom field testsupdated reset (from 0)

3 years ago

Ah, right, maybe it is. I suppose my confusion is because this all worked fine with the exact same config on 7.2 (sssd 1.13.0-40.el7_2.12)... with problems only arising as a result of upgrading to 7.3 - hence my pinning it on this issue. But perhaps it is a timeout issue... thanks, I'll look into it. I get the point about enumeration not being recommended, but we have a fairly small domain and I need to first wean some people off expecting a full output from getent passwd. Cheers.

Try moving the cache to tmpfs or increase the 'timeout' option. If neither helps, consider opening a new ticket, but I'm fairly confident the original issue is not the root cause of your problem.

Metadata Update from @jhrozek:
- Custom field design_review reset (from false)
- Custom field mark reset (from false)
- Custom field review reset (from false)
- Custom field sensitive reset (from false)
- Custom field testsupdated reset (from false)

3 years ago

Thanks, yes, I've changed the timeout option (to 20), and that seems to help. I think I'll only enable enumeration on a selective basis. By the way, can you confirm how many iterations of timeout take place before sssd_be is restarted? Also, I realise also how I ended up at this bug ... I got here via: https://bugzilla.redhat.com/show_bug.cgi?id=1379774 which does seem to describe the symptoms I see.

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