On 2022-04-18 15:48, Takashi Yano wrote:
On Sat, 16 Apr 2022 18:16:50 +0900
Takashi Yano wrote:
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.
I identified the cause and applied a workaround patch.
The countermeasure version is available at:
https://tyan0.yr32.net/cygwin/x86/test/cygwin1-20220418.dll.xz
https://tyan0.yr32.net/cygwin/x86_64/test/cygwin1-20220418.dll.xz
Could you please test?
I've tested the 32-bit version, and Ctrl-C in my original test works as
expected (no deadlock or other issues after multiple tries). Thank you
for the fix!
Alexey
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