Re: Deadlock when pressing Ctrl-C at startup of a native console application

[Takashi Yano <takashi.yano@nifty.ne.jp>]

On Fri, 15 Apr 2022 21:09:05 +0300
Alexey Izbyshev wrote:
> Hi,
> 
> I've discovered that pressing Ctrl-C in a Cygwin ssh session running the 
> following command can cause a deadlock:
> 
> $ while python -c ''; do :; done
> 
> The exact native application doesn't matter here, e.g. "ping -n 1 
> localhost >/dev/null" instead of "python -c ''" also "works".
> 
> The deadlock is most easily triggered when CPU is fully loaded. It takes 
> no more than 20 tries on my machine to hit it (and when I first saw it, 
> it was on the first try).
> 
> When the deadlock is triggered, there are conhost.exe and 
> cygwin-console-helper.exe processes, but there is no python.
> 
> The exact process tree varies depending on Cygwin version. With the 
> vanilla 3.3.4 (the root is bash spawned by sshd):
> 
> bash---bash-+-conhost.exe
>              `-cygwin-console-helper.exe
> 
> With 20220301 snapshot 
> (https://cygwin.com/snapshots/x86/cygwin1-20220301.dll.xz), I get one of 
> the two following trees with an extra conhost.exe process:
> 
> bash---bash-+-conhost.exe
>              |-conhost.exe
>              `-cygwin-console-helper.exe
> 
> or
> 
> bash---bash-+-conhost.exe
>       |      `-cygwin-console-helper.exe
>       `-conhost.exe
> 
> I was testing with 32-bit Cygwin on x64 Windows 10 21H2.

Thanks for the report. I could reproduce the issue.
I also found the current git master does not have this issue,
while cygwin-3_3-branch does.

Now I am identifying which patch solved the issue.
One is obviously:
https://cygwin.com/pipermail/cygwin-patches/2022q2/011870.html
however, this was applied also for cygwin-3_3-branch. Therefore,
another patch also should affect this issue.

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>