lib/49813: dladdr on non-existent address may cause a deadlock

[stassats%gmail.com@localhost]

>Number:         49813
>Category:       lib
>Synopsis:       dladdr on non-existent address may cause a deadlock
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    lib-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Apr 04 17:15:00 +0000 2015
>Originator:     Stas
>Release:        6.1.6
>Organization:
>Environment:
>Description:
In the dladdr function in
http://cvsweb.netbsd.org/bsdweb.cgi/src/libexec/ld.elf_so/rtld.c?rev=1.173.4.1&content-type=text/x-cvsweb-markup
(can't figure out how to link to a specific line, here's a github link: https://github.com/jsonn/src/blob/c44251ea512cf59e9825553cb119f9eeeacfd250/libexec/ld.elf_so/rtld.c#L1270-1272 )

presumably, it should be lookup_mutex_exit, not _enter, otherwise it will cause a deadlock.
>How-To-Repeat:
#include <dlfcn.h>
#include <stdlib.h>

int main ()
{
  Dl_info dlinfo;
  dladdr(1234, &dlinfo);
  exit(0);
}

=>

#0  0x00007f7ff7c0d51a in ___lwp_park50 () from /usr/libexec/ld.elf_so
#1  0x00007f7ff7c0582c in _rtld_exclusive_enter () from /usr/libexec/ld.elf_so
#2  0x00007f7ff7c06dae in _rtld_exit () from /usr/libexec/ld.elf_so
#3  0x00007f7ff78cc0e7 in __cxa_finalize () from /usr/lib/libc.so.12
#4  0x00007f7ff78cbe3e in exit () from /usr/lib/libc.so.12
#5  0x000000000040095f in main ()
>Fix: