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Wed, 28 Oct 2026 09:45:07 -0700 (PDT) Received: from xps16 ([96.43.243.2]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-85b20216828sm2416941a34.19.2026.10.28.09.45.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Oct 2026 09:45:06 -0700 (PDT) From: Jens Axboe To: linux-block@vger.kernel.org Cc: Chris Mason , "Md. Haris Iqbal" , Jack Wang , Jens Axboe Subject: [PATCH 40/98] rnbd-srv: publish the sess_dev at the end of OPEN Date: Wed, 28 Oct 2026 10:41:43 -0600 Message-ID: <20261028164415.1262013-41-axboe@kernel.dk> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028164415.1262013-1-axboe@kernel.dk> References: <20261028164415.1262013-1-axboe@kernel.dk> X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Chris Mason rnbd_sess_dev_alloc() stores the empty sess_dev in the XArray as its first step. An IO message with the new ID from another connection can find it before bdev_file is set, or hold a reference while a failing OPEN frees it after a mere RCU grace period. Both are reachable from any host that can open a device. Reserve the ID with a NULL entry and store the sess_dev once nothing can fail anymore. The error path still erases the ID, and no longer needs synchronize_rcu(). Fixes: 2de6c8de192b ("block/rnbd: server: main functionality") Cc: "Md. Haris Iqbal" Cc: Jack Wang Signed-off-by: Chris Mason Signed-off-by: Jens Axboe --- drivers/block/rnbd/rnbd-srv.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/block/rnbd/rnbd-srv.c b/drivers/block/rnbd/rnbd-srv.c index 1cfa2c580759..1c80e8fe0267 100644 --- a/drivers/block/rnbd/rnbd-srv.c +++ b/drivers/block/rnbd/rnbd-srv.c @@ -431,7 +431,7 @@ static struct rnbd_srv_sess_dev if (!sess_dev) return ERR_PTR(-ENOMEM); - error = xa_alloc(&srv_sess->index_idr, &sess_dev->device_id, sess_dev, + error = xa_alloc(&srv_sess->index_idr, &sess_dev->device_id, NULL, xa_limit_32b, GFP_NOWAIT); if (error < 0) { pr_warn("Allocating idr failed, err: %d\n", error); @@ -802,6 +802,13 @@ static int process_msg_open(struct rnbd_srv_session *srv_sess, list_add(&srv_sess_dev->dev_list, &srv_dev->sess_dev_list); mutex_unlock(&srv_dev->lock); + /* + * Nothing fails from here on, so let I/O messages find the sess_dev. + * The ID is reserved, so this store allocates nothing. + */ + xa_store(&srv_sess->index_idr, srv_sess_dev->device_id, srv_sess_dev, + GFP_KERNEL); + rnbd_srv_info(srv_sess_dev, "Opened device '%s'\n", srv_dev->name); kfree(full_path); @@ -813,7 +820,6 @@ static int process_msg_open(struct rnbd_srv_session *srv_sess, free_srv_sess_dev: xa_erase(&srv_sess->index_idr, srv_sess_dev->device_id); - synchronize_rcu(); kfree(srv_sess_dev); srv_dev_put: if (open_msg->access_mode != RNBD_ACCESS_RO) { -- 2.56.0