From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by smtp.subspace.kernel.org (Postfix) with ESMTPS id DD3C01CAA65;
	Sat, 31 Jan 2026 01:16:39 +0000 (UTC)
Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173
ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116;
	t=1769822202; cv=none; b=AjMqjfqOc0VR9vme9MhFKQNQW9VQSVBcHRUTXy/OrjNcRsV8vr8NqBQBAYAnKTWipjHYyN3Y3PUJekAWbTB2pJXgSFtB350TtPS9bls5a5KL0m33RiZNDUfj/mj5A4Ekzl9+IfE5CwCjnHSteAF4F2YvBf4IYluVc8UbH1yl9Bk=
ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org;
	s=arc-20240116; t=1769822202; c=relaxed/simple;
	bh=s7cpkxammNxh6+d5d+3bqKdN3SPq8TpxVvWIZ8ZCcjI=;
	h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version:
	 Content-Type:Content-Disposition:In-Reply-To; b=ZGYifQvBqHVSExSqbiLpMkqMM1bgPCOEC32hAVTVA8c6ossIh9ZtGVUY+VKFrJ3kZk1YeDOdh8oR1yhpUFulIsdYZHNz51qK1Ubbm9Yit6Q0cXD9Qpuz14lzJeUpNtwTlR1IJzcz59SNP6RVmVJdkLD2OBELHnWFUIvNZXdfzL4=
ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=XqfXg1dJ; arc=none smtp.client-ip=62.89.141.173
Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk
Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk
Authentication-Results: smtp.subspace.kernel.org;
	dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="XqfXg1dJ"
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
	d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type:
	MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To:
	Content-Transfer-Encoding:Content-ID:Content-Description;
	bh=4hGbcJX/zGCic8102G9qCIKZXSgkfeWlTMil/4Iaml4=; b=XqfXg1dJojWAta23wVrVGw8AbM
	T4YFUEpAGNRy8GVl2crq0/yviLHSn1RwjY7OLNXFUr7MBlJZLFlel+DfkeASAyFuazuY5gYbkZg3C
	r1X86wcMyDCgxj5D/ys/gdAHSFU7r5iSYp0zd049hk3wpBrFCur24CjExKXdOvqJN9VuHv/iRjxzx
	kX5RrybEcEtWMX2qA0ottyCV7wKy8E6VDoLBwHqezT7iyteAdLuRpPADA5DDr5S896BrFSnJfOEmd
	6JvaRmn5kwFYAVnGs71LXmLojX97iH8OqHMoKkN+pTlZ5RhbqGi9BrBSkACYzFfu78y9HaeWVKLwd
	KJWr0I9A==;
Received: from viro by zeniv.linux.org.uk with local (Exim 4.99.1 #2 (Red Hat Linux))
	id 1vlzd9-0000000DGbm-14ID;
	Sat, 31 Jan 2026 01:18:31 +0000
Date: Sat, 31 Jan 2026 01:18:31 +0000
From: Al Viro <viro@zeniv.linux.org.uk>
To: Samuel Wu <wusamuel@google.com>
Cc: Greg KH <gregkh@linuxfoundation.org>, linux-fsdevel@vger.kernel.org,
	torvalds@linux-foundation.org, brauner@kernel.org, jack@suse.cz,
	raven@themaw.net, miklos@szeredi.hu, neil@brown.name,
	a.hindborg@kernel.org, linux-mm@kvack.org,
	linux-efi@vger.kernel.org, ocfs2-devel@lists.linux.dev,
	kees@kernel.org, rostedt@goodmis.org, linux-usb@vger.kernel.org,
	paul@paul-moore.com, casey@schaufler-ca.com,
	linuxppc-dev@lists.ozlabs.org, john.johansen@canonical.com,
	selinux@vger.kernel.org, borntraeger@linux.ibm.com,
	bpf@vger.kernel.org, clm@meta.com,
	android-kernel-team <android-kernel-team@google.com>
Subject: Re: [PATCH v4 00/54] tree-in-dcache stuff
Message-ID: <20260131011831.GZ3183987@ZenIV>
References: <CAG2Kctoo=xiVdhRZnLaoePuu2cuQXMCdj2q6L-iTnb8K1RMHkw@mail.gmail.com>
 <20260128045954.GS3183987@ZenIV>
 <CAG2KctqWy-gnB4o6FAv3kv6+P2YwqeWMBu7bmHZ=Acq+4vVZ3g@mail.gmail.com>
 <20260129032335.GT3183987@ZenIV>
 <20260129225433.GU3183987@ZenIV>
 <CAG2KctoNjktJTQqBb7nGeazXe=ncpwjsc+Lm+JotcpaO3Sf9gw@mail.gmail.com>
 <20260130070424.GV3183987@ZenIV>
 <CAG2Kctoqja9R1bBzdEAV15_yt=sBGkcub6C2nGE6VHMJh13=FQ@mail.gmail.com>
 <20260130235743.GW3183987@ZenIV>
 <CAG2KctotL+tpHQMWWAFOQEy=3NX-7fa9YroqsjnxKmTuunJ2AQ@mail.gmail.com>
Precedence: bulk
X-Mailing-List: linux-usb@vger.kernel.org
List-Id: <linux-usb.vger.kernel.org>
List-Subscribe: <mailto:linux-usb+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:linux-usb+unsubscribe@vger.kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAG2KctotL+tpHQMWWAFOQEy=3NX-7fa9YroqsjnxKmTuunJ2AQ@mail.gmail.com>
Sender: Al Viro <viro@ftp.linux.org.uk>

On Fri, Jan 30, 2026 at 05:05:34PM -0800, Samuel Wu wrote:

> > How lovely...  Could you slap
> >         WARN_ON(ret == -EAGAIN);
> > right before that
> >         if (ret < 0)
> >                 return ret;
> 
> Surprisingly ret == 0 every time, so no difference in dmesg logs with
> this addition.

What the hell?  Other than that mutex_lock(), the only change in there
is the order of store to file->private_data and call of ffs_data_opened();
that struct file pointer is not visible to anyone at that point...

Wait, it also brings ffs_data_reset() on that transition under ffs->mutex...
For a quick check: does
git fetch git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git for-wsamuel2
git switch --detach FETCH_HEAD
demonstrate the same breakage?