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Date: Mon, 27 Jun 2022 16:29:11 +0200
From: Markus Wichmann <nullplan@....net>
To: musl@...ts.openwall.com
Cc: Nick Peng <pymumu@...il.com>
Subject: Re: BUG: Calling readdir/dirfd after vfork will cause
deadlock.
On Mon, Jun 27, 2022 at 12:05:41PM +0800, Nick Peng wrote:
> The feature I want to achieve is to close all file handles after fork to
> avoid file handles being inherited to child processes.
>
The normal solution to that problem is FD_CLOEXEC. I have started just
opening all FDs with FD_CLOEXEC set. If I want to bestow it upon a child
process, I can always dup() it (which clears FD_CLOEXEC from the
destination FD).
> In order to avoid file handles inheriting from child processes, we
> implemented a API like system,close all file handles after vfork.
That wouldn't be conforming to the vfork() spec either, since close() is
neither _exit() nor in the exec* family.
> The component is based on glibc, currently this program runs for about 10
> years without deadlock.
> Recently, this component is used in musl-based embedded systems, and it
> hangs often.
>
Congratulations, you found a way to make undefined behavior break your
setup only a decade after its inception. Such is the nature of the
beast. Sometimes it will work for you. Until something changes, that may
be out of your control.
Ciao,
Markus
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