DMARC-Filter: OpenDMARC Filter v1.4.2 delorie.com 4AKDiCgc3637163
Authentication-Results: delorie.com; dmarc=pass (p=none dis=none) header.from=cygwin.com
Authentication-Results: delorie.com; spf=pass smtp.mailfrom=cygwin.com
DKIM-Filter: OpenDKIM Filter v2.11.0 delorie.com 4AKDiCgc3637163
Authentication-Results: delorie.com;
	dkim=pass (1024-bit key, unprotected) header.d=cygwin.com header.i=@cygwin.com header.a=rsa-sha256 header.s=default header.b=rfx/TjbU
X-Recipient: archive-cygwin AT delorie DOT com
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org C83B03858416
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1732110250;
	bh=Y0EAfEgURseHmSNKsLHVs48mYqRD+vAckrJ5hpTNr7I=;
	h=Date:To:Subject:In-Reply-To:References:List-Id:List-Unsubscribe:
	 List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:
	 From;
	b=rfx/TjbUI9Xy8Y6pA70XElpTBEEQD2siB1idml0vMKL4VEHUs2KPY/VpMCTOTRaHW
	 AhiFZDe+WE0JMt+c8q90YWqLR9lMCKBvT/+9uPiFIptNIvd5KJ3lCHiLvAbb2DmJp0
	 mrcTbuQMCbvhVGC0YIYA8HJh/vDrGiLqDrDPVSb0=
X-Original-To: cygwin AT cygwin DOT com
Delivered-To: cygwin AT cygwin DOT com
DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 7529D3858D38
ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 7529D3858D38
ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1732110192; cv=none;
 b=WuImhvxaf6C0Ph1PiAZvFhiKVa8w1CfrhS/W4A/Y2n/4sDsnau8kPMKa2HkSoMf8B1Va4goJpnYISExyPaprUiXybLH8GSP8y+JqbFbzxwrwefJk6CJjCFcGhKyl70RXT1iKS+NodQeysxiPKG4crMB84dSY7dVt5hrA7NUq/UA=
ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key;
 t=1732110192; c=relaxed/simple;
 bh=RZ5p9djceQKhg9C78Bjx7q56M7fo4pYZkmyHa0CEGs8=;
 h=Date:From:To:Subject:Message-Id:Mime-Version:DKIM-Signature;
 b=ExRXEih/8s7KLJuhlRUqDWB5S0GHXnYZxFBpZ8OpAIv2ssuL366/dnT/InCp1sKha/sLuQbeFPr6P/7IqdKFtp2ZCsxtztMWBvi42Y9aJM6evE8+FWbUrB3LtYGlZucrpAv0uX6VCXT49NBjN817xNuaGvBhRsmfRmJb9EoUkzg=
ARC-Authentication-Results: i=1; server2.sourceware.org
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 7529D3858D38
Date: Wed, 20 Nov 2024 22:43:08 +0900
To: cygwin AT cygwin DOT com
Subject: Re: SIGKILL may no longer work after many SIGCONT/SIGSTOP signals
Message-Id: <20241120224308.000a18e48c0b8926e82e5147@nifty.ne.jp>
In-Reply-To: <20241119182152.c2195f50ed7091fbed644606@nifty.ne.jp>
References: <adc78776-84f6-82bc-13b4-3a51b11027fa AT t-online DOT de>
 <20241119182152 DOT c2195f50ed7091fbed644606 AT nifty DOT ne DOT jp>
X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.30; i686-pc-mingw32)
Mime-Version: 1.0
X-BeenThere: cygwin AT cygwin DOT com
X-Mailman-Version: 2.1.30
Precedence: list
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe: <https://cygwin.com/mailman/options/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive: <https://cygwin.com/pipermail/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe: <https://cygwin.com/mailman/listinfo/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Errors-To: cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com
Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>

On Tue, 19 Nov 2024 18:21:52 +0900
Takashi Yano wrote:
> On Tue, 12 Nov 2024 10:53:58 +0100
> Christian Franke wrote:
> > Found with 'stress-ng --cpu-sched' from current stress-ng upstream HEAD:
> > 
> > Testcase (attached):
> > 
> > $ gcc -O2 -o manysignals manysignals.c
> > 
> > $ ./manysignals
> > fork() = 1833
> > ...
> > fork() = 1848
> > ...
> > kill(1833, 17)
> > ...
> > kill(1848, 17)
> > kill(1833, 9)
> > ...
> > kill(1848, 9)
> > waitpid(1833, ., 0)
> > 
> > 
> > Run this in second terminal:
> > 
> > $ watch "ps | sed -n '1p;/manysignals/{/sed/d;p}'"
> > 
> > If 'S' appear in the first column, the child processes likely reached 
> > the final SIGSTOP state. This takes some time. The parent process may 
> > still hang in first waitpid() but should not.
> > 
> > If the parent process is aborted with ^C, child processes may be stopped 
> > or left behind. Occasionally a child process that can not be stopped by 
> > Cygwin (kill -9) is left behind.
> > 
> > Tested with ancient (i7-2600K) and more recent (i7-14700K) CPU :-)
> > 
> > 
> > Unrelated to the above, but related to 'stress-ng --cpu-sched' which 
> > uses sched_get/setscheduler():
> > 
> > - sched_getscheduler() always returns SCHED_FIFO. As far as I understand 
> > Linux sched(7), this is a non-preemptive real-time policy. The 
> > preemptive SCHED_RR would possibly a more reasonable value. 
> > Unfortunately SCHED_OTHER cannot be used because it would require to 
> > ignore the priority.
> > 
> > - sched_setscheduler() always fails with ENOSYS. It IMO should allow to 
> > set 'param->sched_priority' if 'policy' is equal to the value returned 
> > by sched_getscheduler().
> 
> Thanks for the report and the test case. I'm now looking into
> the issue. Please wait a while.

Hopefully, I have found the cause.

The deadlock happens between main thread and wait_sig thread.
The main thread is waiting for the wait_sig thread triggering
wakeup event while the wait_sig thread is waiting previous
signal being processed by main thread.

Let me consider how to fix that.

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

-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple