In postmaster.c signal handler pmdie() calls ereport() and
errmsg_internal(), which could call palloc() then malloc() if
necessary. Because it is possible that pmdie() gets called while
malloc() gets called in postmaster, I think it is possible that a
deadlock situation could occur through an internal locking inside
malloc(). I have not observed the exact case in PostgreSQL but I see a
suspected case in Pgpool-II. In the stack trace #14, malloc() is
called by Pgpool-II. It is interrupted by a signal in #11, and the
signal handler calls malloc() again, and it is stuck at #0.
So my question is, is my concern about PostgreSQL valid?
If so, how can we fix it?
#0 __lll_lock_wait_private () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:95
#1 0x00007f67fe20ccba in _L_lock_12808 () from /lib/x86_64-linux-gnu/libc.so.6
#2 0x00007f67fe20a6b5 in __GI___libc_malloc (bytes=15) at malloc.c:2887
#3 0x00007f67fe21072a in __GI___strdup (s=0x7f67fe305dd8 "/etc/localtime") at strdup.c:42
#4 0x00007f67fe239f51 in tzset_internal (always=<optimized out>, explicit=explicit@entry=1) at tzset.c:444
#5 0x00007f67fe23a913 in __tz_convert (timer=timer@entry=0x7ffce1c1b7f8, use_localtime=use_localtime@entry=1,
tp=tp@entry=0x7f67fe54bde0<_tmbuf>) at tzset.c:632
#6 0x00007f67fe2387d1 in __GI_localtime (t=t@entry=0x7ffce1c1b7f8) at localtime.c:42
#7 0x000000000045627b in log_line_prefix (buf=buf@entry=0x7ffce1c1b8d0, line_prefix=<optimized out>,
edata=<optimizedout>) at ../../src/utils/error/elog.c:2059
#8 0x000000000045894d in send_message_to_server_log (edata=0x753320 <errordata>) at
../../src/utils/error/elog.c:2084
#9 EmitErrorReport () at ../../src/utils/error/elog.c:1129
#10 0x0000000000456d8e in errfinish (dummy=<optimized out>) at ../../src/utils/error/elog.c:434
#11 0x0000000000421f57 in die (sig=2) at protocol/child.c:925
#12 <signal handler called>
#13 _int_malloc (av=0x7f67fe546760 <main_arena>, bytes=4176) at malloc.c:3302
#14 0x00007f67fe20a6c0 in __GI___libc_malloc (bytes=4176) at malloc.c:2891
Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp