strace -f hangs forever with process who creates child process

strace -f hangs forever with process who creates child process

[Qian Hong]

Dear list,

I just found `strace -f` hangs forever for me.

$ uname -a
CYGWIN_NT-6.1 fracting-PC 2.2.1(0.289/5/3) 2015-08-15 11:00 i686 Cygwin)

$ cat parent.sh
./child.sh

$ cat child.sh
echo haha

$ strace -f -o out.txt bash -c parent.sh #hangs forever.

I have a few C source test case here, which were originally for a Wine
bug, but could reproduce this Cygwin bug:
https://bugs.wine-staging.com/show_bug.cgi?id=525#c2

To reproduce:
(Ignore the Wine bug report itself, just copy the source. The Wine bug
itself is fixed now, with analysis which indicates something is wrong
with IsDebuggerPresent(). I refer the bug here since it might help to
triage our Cygwin issue if there is something related)

gcc spawn-parent.c -o spawn-parent.exe
gcc spawn-child.c -o spawn-child.exe
gcc dummy.c -o dummy.exe

Without strace, the above programs works fine:
$ ./spawn-parent.exe
from SPAWN parent!
from SPAWN dummy!
haha this is dummy

However, when tracing with `strace -f`, spawn-child.exe hangs:
$ strace -f -o /tmp/spawn.nested.strace.txt ./spawn-parent.exe #hangs



I read the strace document of Cygwin[1], it said:

  -f, --trace-children         trace child processes (toggle - default true)

[1] https://cygwin.com/cygwin-ug-net/strace.html

According to my test, `strace` without `-f` works fine, which trace
child process, as the document says.

Is it a known bug that toggle off child process doesn't work? Or did i
miss anything else?

(Note, current strace works with my needs, I don't need to toggle off
child process tracing at all, just make sure there is not a bug here)

Thanks!


-- 
Regards,
Qian Hong

-
http://www.winehq.org

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RE: strace -f hangs forever with process who creates child process

[Nellis, Kenneth]

From: Qian Hong
> I just found `strace -f` hangs forever for me.
> 
> $ uname -a
> CYGWIN_NT-6.1 fracting-PC 2.2.1(0.289/5/3) 2015-08-15 11:00 i686 Cygwin)
> 
> $ cat parent.sh
> ./child.sh
> 
> $ cat child.sh
> echo haha
> 
> $ strace -f -o out.txt bash -c parent.sh #hangs forever.

FWIW, this also seems to hang for me, but can't confirm that it 
hangs "forever", as I didn't wait that long. Ctrl/C-ing out works, 
but that takes several seconds to take effect. And then I can't 
delete out.txt:

$ rm -f out.txt
rm: cannot remove ‘out.txt’: Device or resource busy
$ 

Commands 'ps' and 'who' don't indicate any other processes, but
Task Manager shows another bash process. After killing that process
I am then able to delete out.txt.

--Ken Nellis

Re: strace -f hangs forever with process who creates child process

[Roger Wells]

On 08/24/2015 09:05 AM, Nellis, Kenneth wrote:
> From: Qian Hong
>> I just found `strace -f` hangs forever for me.
>>
>> $ uname -a
>> CYGWIN_NT-6.1 fracting-PC 2.2.1(0.289/5/3) 2015-08-15 11:00 i686 Cygwin)
>>
>> $ cat parent.sh
>> ./child.sh
>>
>> $ cat child.sh
>> echo haha
>>
>> $ strace -f -o out.txt bash -c parent.sh #hangs forever.
> 
> FWIW, this also seems to hang for me, but can't confirm that it 
> hangs "forever", as I didn't wait that long. Ctrl/C-ing out works, 
> but that takes several seconds to take effect. And then I can't 
> delete out.txt:
> 
> $ rm -f out.txt

I also can confirm this on the same cygwin release but for x86_64:

uname -a
CYGWIN_NT-6.1 rwells-x220 2.2.1(0.289/5/3) 2015-08-20 11:42 x86_64 Cygwin



-- 
Roger Wells, P.E.
leidos
221 Third St
Newport, RI 02840
401-847-4210 (voice)
401-849-1585 (fax)
roger.k.wells@leidos.com

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Re: strace -f hangs forever with process who creates child process

[Corinna Vinschen]

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On Aug 24 09:37, Roger Wells wrote:
> On 08/24/2015 09:05 AM, Nellis, Kenneth wrote:
> > From: Qian Hong
> >> I just found `strace -f` hangs forever for me.
> >>
> >> $ uname -a
> >> CYGWIN_NT-6.1 fracting-PC 2.2.1(0.289/5/3) 2015-08-15 11:00 i686 Cygwin)
> >>
> >> $ cat parent.sh
> >> ./child.sh
> >>
> >> $ cat child.sh
> >> echo haha
> >>
> >> $ strace -f -o out.txt bash -c parent.sh #hangs forever.
> > 
> > FWIW, this also seems to hang for me, but can't confirm that it 
> > hangs "forever", as I didn't wait that long. Ctrl/C-ing out works, 
> > but that takes several seconds to take effect. And then I can't 
> > delete out.txt:
> > 
> > $ rm -f out.txt
> 
> I also can confirm this on the same cygwin release but for x86_64:

No more metoos required, thank you.  It's a generic problem when trying
to trace forking/spawning parents without also tracing their children.

Having said that, I don't know what the cause is, but I guess that
"nobody did it" for a while.  Also, "don't do that" for now ;)


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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Re: strace -f hangs forever with process who creates child process

[Corinna Vinschen]

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On Aug 24 16:03, Corinna Vinschen wrote:
> On Aug 24 09:37, Roger Wells wrote:
> > On 08/24/2015 09:05 AM, Nellis, Kenneth wrote:
> > > From: Qian Hong
> > >> I just found `strace -f` hangs forever for me.
> > >>
> > >> $ uname -a
> > >> CYGWIN_NT-6.1 fracting-PC 2.2.1(0.289/5/3) 2015-08-15 11:00 i686 Cygwin)
> > >>
> > >> $ cat parent.sh
> > >> ./child.sh
> > >>
> > >> $ cat child.sh
> > >> echo haha
> > >>
> > >> $ strace -f -o out.txt bash -c parent.sh #hangs forever.
> > > 
> > > FWIW, this also seems to hang for me, but can't confirm that it 
> > > hangs "forever", as I didn't wait that long. Ctrl/C-ing out works, 
> > > but that takes several seconds to take effect. And then I can't 
> > > delete out.txt:
> > > 
> > > $ rm -f out.txt
> > 
> > I also can confirm this on the same cygwin release but for x86_64:
> 
> No more metoos required, thank you.  It's a generic problem when trying
> to trace forking/spawning parents without also tracing their children.
> 
> Having said that, I don't know what the cause is, but I guess that
> "nobody did it" for a while.  Also, "don't do that" for now ;)

Please try the latest developer snapshot from https://cygwin.com/snapshots/
It should fix the issue.


Thanks,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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Re: strace -f hangs forever with process who creates child process

[Qian Hong]

Hi Corinna,

On Tue, Aug 25, 2015 at 12:50 AM, Corinna Vinschen
<corinna-cygwin@cygwin.com> wrote:
> Please try the latest developer snapshot from https://cygwin.com/snapshots/
> It should fix the issue.

Thanks very much for the fix. I've retested on both Win7 and Wine
(Wine Staging 1.7.50), and I can confirm now `strace -f` works fine on
both platform. No longer hangs, also child process is not traced.

Thanks!


-- 
Regards,
Qian Hong

-
http://www.winehq.org

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Re: strace -f hangs forever with process who creates child process

[Corinna Vinschen]

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On Aug 25 11:18, Qian Hong wrote:
> Hi Corinna,
> 
> On Tue, Aug 25, 2015 at 12:50 AM, Corinna Vinschen
> <corinna-cygwin@cygwin.com> wrote:
> > Please try the latest developer snapshot from https://cygwin.com/snapshots/
> > It should fix the issue.
> 
> Thanks very much for the fix. I've retested on both Win7 and Wine
> (Wine Staging 1.7.50), and I can confirm now `strace -f` works fine on
> both platform. No longer hangs, also child process is not traced.

Thanks for testing!


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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