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From: "xujing99 at huawei dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug admin/28331] Multi-threaded exec pthread_create and dlopen may
 cause deadlock
Date: Mon, 13 Sep 2021 02:59:13 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D28331

--- Comment #1 from xujing <xujing99 at huawei dot com> ---
If I have a c++ dynamic library(named libA.so) that contains a global objec=
t,
the global object will call the post-constructor at initialization and hold
it's own lock(named A_lock) when dlopen loads libA.so. Assume that two thre=
ads
execute the following process=EF=BC=9A
    Thread1:dlopen(libA.so) =3D> hold dl_load_lock =3D> load libA.so =3D> i=
nit global=20
            object from libA.so =3D> wait for hold A_lock
    Thread2:my own code hold A_lock =3D> pthread_create =3D> _dl_allocate_t=
ls_init=20
            =3D> wait for hold dl_load_lock
In this case, an ABBA deadlock occurs. Is this a bug?

My stack looks like this:
Thread 1 (LWP 136013):
#0  0x00007f57a108510d in ?? () from /usr/lib64/libpthread.so.0
#1  0x00007f57a107e4d1 in pthread_mutex_lock () from /usr/lib64/libpthread.=
so.0
#1  stack waiting for holding A_lock
...
#6  0x00007f5781c1bb8b in LogProcess::Init (strProcName=3D...,
nProcHandle=3DnProcHandle@entry=3D0) at
./service/biz_frame/code/server/src/logging/logprocess.cpp:107
...
#20 0x00007f57a0fef21f in _dl_catch_exception () from /usr/lib64/libc.so.6
#21 0x00007f57a786442b in ?? () from /lib64/ld-linux-x86-64.so.2
#22 0x00007f57a3de2296 in ?? () from /usr/lib64/libdl.so.2
#23 0x00007f57a0fef21f in _dl_catch_exception () from /usr/lib64/libc.so.6
#24 0x00007f57a0fef2af in _dl_catch_error () from /usr/lib64/libc.so.6
#25 0x00007f57a3de2985 in ?? () from /usr/lib64/libdl.so.2
#26 0x00007f57a3de2351 in dlopen () from /usr/lib64/libdl.so.2
...
...
#38 0x00007f57a0fb3520 in clone () from /usr/lib64/libc.so.6

Thread 2 (LWP 134627):
#0  0x00007f57a108510d in ?? () from /usr/lib64/libpthread.so.0
#1  0x00007f57a107e580 in pthread_mutex_lock () from /usr/lib64/libpthread.=
so.0
#2  0x00007f57a7863835 in _dl_allocate_tls_init () from
/lib64/ld-linux-x86-64.so.2
#3  0x00007f57a107cb7c in pthread_create () from /usr/lib64/libpthread.so.0
...
#10 Stack holding A_lock
...
#14 0x0000561689e0d579 in main ()

--=20
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