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From: "dingxiangfei2009 at protonmail dot ch"
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To: glibc-bugs@sourceware.org
Subject: [Bug nptl/25847] pthread_cond_signal failed to wake up
 pthread_cond_wait due to a bug in undoing stealing
Date: Thu, 14 May 2020 08:52:43 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D25847

Ding Xiang Fei <dingxiangfei2009 at protonmail dot ch> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dingxiangfei2009@protonmail
                   |                            |.ch

--- Comment #5 from Ding Xiang Fei <dingxiangfei2009 at protonmail dot ch> =
---
This bug can be reproduced on OCaml applications running on Debian 10 (bust=
er),
where glibc version is 2.28-10, though I think more recent versions of glibc
will be affected as well since the current construction has not been revised
since 2016.

It has the similar symptom with regards to the master lock of OCaml runtime
system. With OCaml version 4.09, the bug is triggered producing the followi=
ng
state of the conditional variable.

{
  __data =3D {
    {
      __wseq =3D 105780454,=20
      __wseq32 =3D {
        __low =3D 105780454,=20
        __high =3D 0
      }
    },=20
    {
      __g1_start =3D 105780438,=20
      __g1_start32 =3D {
        __low =3D 105780438,=20
        __high =3D 0
      }
    },=20
    __g_refs =3D {12, 0},=20
    __g_size =3D {0, 0},=20
    __g1_orig_size =3D 8,=20
    __wrefs =3D 48,=20
    __g_signals =3D {0, 2}
  },=20
  __size =3D "\346\024N\006\000\000\000\000\326\024N\006\000\000\000\000\f",
'\000' <repeats 15 times>,
"\b\000\000\000\060\000\000\000\000\000\000\000\002\000\000",=20
  __align =3D 105780454
}

One signal is pending for G1, while G1 is "empty".

The repro code from Qin also locks up on a Skylake processor, restricted to=
 run
on 4 cores, 100 threads.

--=20
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