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Date:	Sat, 3 Jan 2026 23:05:11 +0900
To:	cygwin AT cygwin DOT com, cygwin-patches AT cygwin DOT com
Subject:	Re: flock deadlock
Message-Id:	<20260103230511.24a6f772323927a141bf595f@nifty.ne.jp>
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From:	Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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On Sun, 28 Dec 2025 11:52:36 -0800
Nahor <nahor.j+cygwin AT gmail DOT com> wrote:
> Attached is a reproducible example.
> The example just calls `fork()` then open/flock/close a directory and
> repeats (fork/open/flock/close). The forks optionally sleep then
> open/flock/close the same directory and exit.
> 
> There is no issue if either the parent or the children don't call `flock()`.
> Without sleeping, the example deadlocks immediately on my system 100%
> of the time. Killing the child allow the parent to proceed, fork the
> next child, which triggers the next deadlock.
> When sleeping, _sometimes_ one child will deadlock with the parent.
> Killing that child allows the parent and remaining children to proceed
> (and potentially trigger another deadlock). Killing the parent also
> unblocks all the children.

Thanks for the report and the test case.
I looked into the issue and found the cause. I also confirmed that
the patch attached solves the issue.

Could anyone please review the patch?

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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