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Date: Tue, 4 Jun 2024 18:06:48 +0200
From: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= <mic@digikod.net>
To: Mark Brown <broonie@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>, 
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jakub Kicinski <kuba@kernel.org>, 
	Kees Cook <keescook@chromium.org>, Linus Torvalds <torvalds@linux-foundation.org>, 
	Sasha Levin <sashal@kernel.org>, Sean Christopherson <seanjc@google.com>, 
	Shengyu Li <shengyu.li.evgeny@gmail.com>, Shuah Khan <shuah@kernel.org>, 
	Shuah Khan <skhan@linuxfoundation.org>, Bagas Sanjaya <bagasdotme@gmail.com>, 
	Brendan Higgins <brendanhiggins@google.com>, David Gow <davidgow@google.com>, 
	"David S . Miller" <davem@davemloft.net>, Florian Fainelli <florian.fainelli@broadcom.com>, 
	=?utf-8?Q?G=C3=BCnther?= Noack <gnoack@google.com>, Jon Hunter <jonathanh@nvidia.com>, Ron Economos <re@w6rz.net>, 
	Ronald Warsow <rwarsow@gmx.de>, Stephen Rothwell <sfr@canb.auug.org.au>, 
	Will Drewry <wad@chromium.org>, kernel test robot <oliver.sang@intel.com>, kvm@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, netdev@vger.kernel.org, 
	stable@vger.kernel.org
Subject: Re: [PATCH v7 04/10] selftests/harness: Fix interleaved scheduling
 leading to race conditions
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On Mon, Jun 03, 2024 at 06:22:32PM +0100, Mark Brown wrote:
> On Mon, Jun 03, 2024 at 05:27:52PM +0100, Mark Brown wrote:
> > On Mon, May 27, 2024 at 08:07:40PM +0100, Mark Brown wrote:
> 
> > > This is now in mainline and appears to be causing several tests (at
> > > least the ptrace vmaccess global_attach test on arm64, possibly also
> > > some of the epoll tests) that previously were timed out by the harness
> > > to to hang instead.  A bisect seems to point at this patch in
> > > particular, there was a bunch of discussion of the fallout of these
> > > patches but I'm afraid I lost track of it, is there something in flight
> > > for this?  -next is affected as well from the looks of it.

Thanks for the heads up.  I warned about not being able to test
everything when fixing kselftest last time, but nobody show up.  Is
there an easy way to run most kselftests?  We really need a (more
accessible) CI...

> 
> > FWIW I'm still seeing this on -rc2...
> 
> AFAICT this is due to the switch to using clone3() with CLONE_VFORK

I guess it started with the previous vfork() that was later replaced
with CLONE_VFORK.

> to start the test which means we never even call alarm() to set up the
> timeout for the test, let alone have the signal for it delivered.  I'm a
> confused about how this could ever work, with clone_vfork() the parent
> shouldn't run until the child execs (which won't happen here) or exits.
> Since we don't call alarm() until after we started the child we never
> actually get that far, but even if we reorder things we'll not get the
> signal for the alarm if the child messes up since the parent is
> suspended.
> 
> I'm not clear what the original race being fixed here was but it seems
> like we should revert this since the timeout functionality is pretty
> important?

It took me a while to fix all the previous issues and it would be much
easier to just fix this issue too.

I'm working on it.