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Date: Mon, 10 Aug 2026 17:40:21 -0600
From: Keith Busch <kbusch@kernel.org>
To: Daniel Wagner <dwagner@suse.de>
Cc: Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
	Chris Leech <cleech@redhat.com>, linux-nvme@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Dmitry Bogdanov <d.bogdanov@yadro.com>,
	Daniel Wagner <wagi@kernel.org>
Subject: Re: [PATCH] nvme-tcp: fix usage of page_frag_cache
Message-ID: <anphZRzJvg0zSE6g@kbusch-mbp>
References: <20260716-nvme-tcp-page_fraq_cache-v1-1-ea660828cf93@kernel.org>
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In-Reply-To: <20260716-nvme-tcp-page_fraq_cache-v1-1-ea660828cf93@kernel.org>

On Thu, Jul 16, 2026 at 04:42:19PM +0200, Daniel Wagner wrote:
> From: Dmitry Bogdanov <d.bogdanov@yadro.com>
> 
> nvme uses page_frag_cache to preallocate PDU for each preallocated request
> of block device. Block devices are created in parallel threads,
> consequently page_frag_cache is used in not thread-safe manner.
> That leads to incorrect refcounting of backstore pages and premature free.

I was struggling to see how the nvme_tcp callback was happening
concurrently for the same queue. It's because you're using an io
scheduler, right? I don't think this applies if you don't have one
enabled.

Anyway, with that understanding, looks like a safe patch. Applied to
nvme-7.3.