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Date: Thu, 23 Oct 2025 22:22:01 +0800
From: Tzung-Bi Shih <tzungbi@kernel.org>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Benson Leung <bleung@chromium.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Danilo Krummrich <dakr@kernel.org>,
	Jonathan Corbet <corbet@lwn.net>, Shuah Khan <shuah@kernel.org>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	chrome-platform@lists.linux.dev, linux-kselftest@vger.kernel.org,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Bartosz Golaszewski <brgl@bgdev.pl>,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Simona Vetter <simona.vetter@ffwll.ch>,
	Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v5 5/7] revocable: Add fops replacement
Message-ID: <aPo6CZyT_IGWmu-O@tzungbi-laptop>
References: <20251016054204.1523139-6-tzungbi@kernel.org>
 <20251016123149.GA88213@nvidia.com>
 <aPGryj-V5PQZRtoI@google.com>
 <20251017134916.GK3901471@nvidia.com>
 <aPJp3hP44n96Rug9@tzungbi-laptop>
 <20251017162116.GA316284@nvidia.com>
 <aPT-7TTgW_Xop99j@tzungbi-laptop>
 <20251020115734.GH316284@nvidia.com>
 <aPcQ99MZse5zmv3o@google.com>
 <20251021121536.GG316284@nvidia.com>
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In-Reply-To: <20251021121536.GG316284@nvidia.com>

On Tue, Oct 21, 2025 at 09:15:36AM -0300, Jason Gunthorpe wrote:
> On Tue, Oct 21, 2025 at 04:49:59AM +0000, Tzung-Bi Shih wrote:
> 
> > I didn't get the idea.  With a mutex, how to handle the opening files?
> > 
> > Are they something like: (?)
> > - Maintain a list for opening files in both .open() and .release().
> > - In misc_deregister_sync(), traverse the list, do something (what?), and
> >   wait for the userspace programs close the files.
> 
> You don't need any list, we don't want to close files.
> 
> Something like this, it is very simple. You can replace the rwsem with
> a srcu. srcu gives faster read locking but much slower sync.
> 
> [...]

I see.  The idea is basically the same but don't use revocable at all.

I was misunderstanding about the "sync" we were discussing for
misc_deregister_sync().  The "sync", is analogous to synchronize_srcu()
of revocable_provider_revoke() in the revocable version [1], doesn't wait
for closing all opened files.

[1] https://lore.kernel.org/chrome-platform/aPT-7TTgW_Xop99j@tzungbi-laptop/