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([2620:10d:c092:600::1:5f66]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48febe6b60csm14137405e9.6.2026.05.15.03.26.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 May 2026 03:26:23 -0700 (PDT) Message-ID: <9732fdae-5e0d-4373-90a6-251d270eae16@gmail.com> Date: Fri, 15 May 2026 11:26:05 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/5] io_uring/zcrx: notify user when out of buffers To: =?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= , io-uring@vger.kernel.org, Jens Axboe Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, netdev@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , Vishwanath Seshagiri , Vishwanath Seshagiri References: <20260422112522.3316660-1-cleger@meta.com> <20260422112522.3316660-2-cleger@meta.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: <20260422112522.3316660-2-cleger@meta.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/22/26 12:25, Clément Léger wrote: > From: Pavel Begunkov ...> static inline struct page *io_zcrx_iov_page(const struct net_iov *niov) > { > struct io_zcrx_area *area = io_zcrx_iov_to_area(niov); > @@ -531,6 +541,7 @@ static struct io_zcrx_ifq *io_zcrx_ifq_alloc(struct io_ring_ctx *ctx) > > ifq->if_rxq = -1; > spin_lock_init(&ifq->rq.lock); > + spin_lock_init(&ifq->ctx_lock); > mutex_init(&ifq->pp_lock); > refcount_set(&ifq->refs, 1); > refcount_set(&ifq->user_refs, 1); > @@ -585,6 +596,11 @@ static void io_zcrx_ifq_free(struct io_zcrx_ifq *ifq) > if (ifq->dev) > put_device(ifq->dev); > > + scoped_guard(spinlock_bh, &ifq->ctx_lock) { > + if (ifq->master_ctx) > + percpu_ref_put(&ifq->master_ctx->refs); > + } > + Something very odd happened here. It's not my patch but rather an edited squash of two other patches. This particular hunk creates a circular dependency, i.e. io_uring waits for this reference to be put down before destroying the zcrx instance that triggers io_zcrx_ifq_free. -- Pavel Begunkov