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Date: Thu, 3 Apr 2025 01:52:16 +0900
To: cygwin AT cygwin DOT com
Subject: Re: Crashes in cmake subprocesses since 3.6.0
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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 Wed, 2 Apr 2025 22:01:25 +0900
Takashi Yano via Cygwin <cygwin AT cygwin DOT com> wrote:

> Hi Corinna,
> 
> On Mon, 31 Mar 2025 11:28:44 +0200
> Corinna Vinschen wrote:
> > On Mar 30 22:58, Jeremy Drake via Cygwin wrote:
> > > On Mon, 31 Mar 2025, Christoph Reiter via Cygwin wrote:
> > > 
> > > > Starting with 3.6.0 when cmake calls into make/ninja/gcc there is a chance of
> > > > that failing, for example like this:
> > > >
> > > > CMake Error: Generator: build tool execution failed, command was:
> > > > /usr/bin/cmake.exe -E env VERBOSE=1 /usr/bin/make.exe -f Makefile
> > > > cmTC_c87e2/fast
> > > >
> > > > * Problem starts with cygwin 3.6.0
> > > 
> > > I've also reproduced this with cygwin 3.7.0-0.19.g6c5537c0298e, but it
> > > doesn't reproduce as readily as with cygwin 3.6.0-1.
> > 
> > Yes, I can reproduce fails as well, but I don't see an easy way to
> > debug this.  Your testcase just fails but runs along afterwards.
> > 
> > I'm completely cmake-illiterate, which isn't a great help either.
> > 
> > Two points:
> > 
> > - It's unlikely that this occurs only with 3.6.0-1 and later.  It's more
> >   likely that it occurs on the way from 3.5 to 3.6.  Unfortunately the
> >   remaining 3.6.0 test builds are only going back to patchlevel 429 or
> >   so.
> > 
> >   Any chance one of you could bisect Cygwin and find out which commit
> >   introduced the problem?
> > 
> > - Also, since this seems to affect certain cmake versions only, can the
> >   cmake maintainers help here, perhaps?
> 
> Currently, I am looking into this problem.
> 
> What I noticed so far is:
> * The problem occurs after the commit 7ed9adb356df.
> * This problem is happen when fhandler_fifo_pipe::raw_write() returns
>   error because cygwait(pipe_mtx, timeout) returns WAIT_FAILED. This seems
>   to happen due to invalid _cygtls::signal_arrived handle for some reason.
> * The following patch solves the issue.
> 
> diff --git a/winsup/cygwin/local_includes/cygtls.h b/winsup/cygwin/local_includes/cygtls.h
> index f67e9136c..82a34aeca 100644
> --- a/winsup/cygwin/local_includes/cygtls.h
> +++ b/winsup/cygwin/local_includes/cygtls.h
> @@ -228,6 +228,9 @@ public: /* Do NOT remove this public: line, it's a marker for gentls_offsets. */
>    bool locked ();
>    HANDLE get_signal_arrived (bool wait_for_lock = true)
>    {
> +    DWORD dummy;
> +    if (signal_arrived && !GetHandleInformation (signal_arrived, &dummy))
> +      signal_arrived = NULL;
>      if (!signal_arrived)
>        {
>  	if (wait_for_lock)
> 
> Of course, this is not the right thing to do, but this clarifies that the
> cause is _cygtis::signal_arrived being invalid even though it is not NULL.
> The reason is not quite sure to me.
> 
> Any idea?

The following patch also can solve the issue. The problem seems
to be related to fork().

Perhaps, the timming of calling _cygtls::fixup_after_fork(), that
clears signal_arrived to NULL, might not be appropriate?

diff --git a/winsup/cygwin/fork.cc b/winsup/cygwin/fork.cc
index 0742ab363..793521314 100644
--- a/winsup/cygwin/fork.cc
+++ b/winsup/cygwin/fork.cc
@@ -446,10 +446,14 @@ frok::parent (volatile char * volatile stack_here)
       impure_beg = _impure_ptr;
       impure_end = _impure_ptr + 1;
     }
+  HANDLE signal_arrived_back;
+  signal_arrived_back = _my_tls.signal_arrived;
+  _my_tls.signal_arrived = NULL;
   rc = child_copy (hchild, true, !*with_forkables,
 		   "stack", stack_here, ch.stackbase,
 		   impure, impure_beg, impure_end,
 		   NULL);
+  _my_tls.signal_arrived = signal_arrived_back;
 
   __malloc_unlock ();
   locked = false;


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

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