Deadlock of the process tree when running make

Alexey Izbyshev izbyshev@ispras.ru
Sat Apr 16 13:21:34 GMT 2022


On 2022-04-16 12:39, Takashi Yano wrote:
> I am not sure yet what is essential, but the current code closes
> pseudo console only if there is no other process which is attaching
> to the pseudo console. I wonder why javac.exe is remaining as
> zombie. The parent bash.exe calls ColosePseudoConsole() when
> child non-cygwin app is terminated, i.e., after WaitForSingleObject()
> for child process handle returns.
> https://www.cygwin.com/git/?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/spawn.cc;h=81dba5a941e919ea2514013069aef22c6fad8004;hb=7ac0767053e278f0ce9811bf6f77278bd2f49c20#l1009
> 
> What does the "zombie" mean? Is it listed in the process list of
> ProcessHacker? I still suspect that the zombie javac.exe holds
> the  hWritePipe handle leaked from parent bash.exe.
> 
By "zombie" I meant the same thing as in the Linux kernel: a data 
structure that remains after a process terminated, but hasn't been 
waited for yet (I don't know how this is implemented in Cygwin). So 
there is no javac.exe process in ProcessHacker, but "ps" and similar 
tools in Cygwin still list "javac".

I'm now trying to create a small reproducer that I can share, and I've 
had a first small success this night: I could get a very similar hang 
with a simple Makefile and a script with Cygwin 3.3.4. Here is the tree:

make(14479)-+-bash(14484)---bash(14611)
             |-bash(14515)---bash(14618)
             |-bash(14491)---bash(14500)---bash(14612)
             |-bash(14501)---bash(14510)---bash(14605)
             |-bash(14505)---bash(14607)
             |-bash(14494)---bash(14617)
             |-bash(14506)---bash(14513)---bash(14610)
             |-bash(14512)---bash(14518)---bash(14615)
             |-bash(14486)---bash(14495)---bash(14606)
             |-bash(14483)---bash(14490)---bash(14609)
             |-bash(14509)---bash(14614)
             |-bash(14489)---bash(14608)
             |-bash(14499)---bash(14613)
             |-bash(14481)---bash(14485)---python(14588)
             |-bash(14496)---bash(14504)---bash(14616)
             `-bash(14482)---bash(14604)


"python" is a zombie, just as "javac" is in the original case. There is 
also a single "conhost.exe" again, and all of its 5 threads are doing 
the same things as in the original case (including the signal pipe 
thread trying to EnterCriticalSection()). The only difference is that 
leaf bash.exe are trying to acquire pcon mutex at a different point [1], 
but I guess this difference is not important.

I'll try this reproducer with your patched DLL as well as on another 
machine and share it in case of success.

Thanks,
Alexey

[1] 
https://www.cygwin.com/git?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/spawn.cc;h=81dba5a941e919ea2514013069aef22c6fad8004;hb=cygwin-3_3_4-release#l697


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