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Date:      Tue, 17 Oct 2023 16:07:16 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 274535] vlc(1) from Focal hangs on futex
Message-ID:  <bug-274535-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D274535

            Bug ID: 274535
           Summary: vlc(1) from Focal hangs on futex
           Product: Base System
           Version: 15.0-CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: trasz@FreeBSD.org

VLC from amd64 Ubuntu Focal "hangs" on futex on startup.  VLC from a previo=
us
version (Bionic) doesn't exhibit this problem.

Running under strace(1) shows the following:

mmap(NULL, 16488, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 4, 0) =3D 0x804f880=
00
mmap(0x804f89000, 4096, PROT_READ|PROT_EXEC,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 4, 0x1000) =3D 0x804f89000
mmap(0x804f8a000, 4096, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 4,
0x2000) =3D 0x804f8a000
mmap(0x804f8b000, 8192, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 4, 0x2000) =3D 0x804f8b000
close(4)                                =3D 0
mprotect(0x804f8b000, 4096, PROT_READ)  =3D 0
futex(0x80224ede8, FUTEX_WAKE_PRIVATE, 2147483647) =3D 0
futex(0x10b75b0, FUTEX_WAIT_BITSET_PRIVATE, 0, {tv_sec=3D0, tv_nsec=3D0},
FUTEX_BITSET_MATCH_ANYstrace: detach: tkill(2718,0): Invalid argument
strace: Process 2718 detached
 <detached ...>

Note that there are other applications hanging on futex, notably glxinfo(1)=
.=20
The strange thing is, the same glxinfo works when run under strace(1) or
FreeBSD's native ktrace(1).  Race condition of some kind?

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