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From: Keith Busch <kbusch@kernel.org>
To: Qiliang Yuan <odys.yuan@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] nvmet: drop the extra RCU grace period in nvmet_ns_disable()
Date: Wed, 4 Nov 2026 09:35:11 -0700	[thread overview]
Message-ID: <autev0xlCzBMz7SC@kbusch-mbp> (raw)
In-Reply-To: <20261104-bug-nvmet-ns-disable-rcu-v2-1-b158a59318ad@gmail.com>

On Wed, Nov 04, 2026 at 01:31:28AM -0500, Qiliang Yuan wrote:
> nvmet_ns_disable() kills the namespace's percpu ref, waits in
> synchronize_rcu() for anyone looking the namespace up under
> rcu_read_lock(), and then waits for the ref to drop to zero.
> 
> Killing a percpu ref that is still in percpu mode, as the namespace
> ref always is until then, switches it to atomic mode from an RCU
> callback, so the ref can't drop to zero before a grace period has
> passed since the kill. synchronize_rcu() thus adds a second grace
> period in a row, about 4 ms here, and disabling the namespaces of a
> subsystem one by one takes about 9 ms each.
> 
> Drop synchronize_rcu() and rely on the wait for the ref to cover the
> RCU readers as well.

Thanks, applied to nvme-7.4.

      parent reply	other threads:[~2026-11-04 16:35 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-11-04  6:31 Qiliang Yuan
2026-11-04  7:14 ` Christoph Hellwig
2026-11-04 16:35 ` Keith Busch [this message]

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