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From: "fweimer at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug stdio/15142] Missing locking in _IO_cleanup
Date: Wed, 13 Mar 2024 10:23:23 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D15142

--- Comment #7 from Florian Weimer <fweimer at redhat dot com> ---
(In reply to Dmitry Vyukov from comment #6)
> We started getting hangs on the following program:
>=20
> https://github.com/llvm/llvm-project/blob/
> 995d1d114e4e4ff708a03cdb0a975209c6197f9f/compiler-rt/test/tsan/
> getline_nohang.cpp#L28
>=20
> Basically just calls a blocking getline in one thread and another thread
> tries to exit.

It's blocking on this:

  FILE *stream =3D fdopen(fd[0], "r");
  while (1) {
    volatile int res =3D getline(&line, &size, stream);
    (void)res;
  }

It's not a writable stream, so we could avoid the blocking with a more comp=
lex
handshake between stdio streams and exit. I'm not sure if it's worth doing
that.  We could perhaps add another flag to fopen/fdopen that indicates that
the stream should not participate in fflush (NULL) or exit flushing.

For streams which are blocked in writing, POSIX does not really give us a w=
ay
to make forward progress because we have to flush the unwritten data before
exiting.

--=20
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