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Wed, 16 Sep 2026 15:10:33 +0000 (GMT) Received: from li-a84c74cc-2b13-11b2-a85c-acdd023f0674.ibm.com.com (unknown [9.61.52.228]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 16 Sep 2026 15:10:33 +0000 (GMT) From: Nilay Shroff To: hch@lst.de, kbusch@kernel.org, sagi@grimberg.me, kch@nvidia.com Cc: linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, gjoyce@linux.ibm.com, Nilay Shroff Subject: [PATCH 2/2] nvmet: don't allow I/O admission after percpu ns reference is killed Date: Wed, 16 Sep 2026 20:40:00 +0530 Message-ID: <20260916151012.3702896-3-nilay@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260916151012.3702896-1-nilay@linux.ibm.com> References: <20260916151012.3702896-1-nilay@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTE2MDIwNCBTYWx0ZWRfX9AyQMTC/Sczo aNWfdl02ezkbAk9eRO7cK652SlupP1yzWVE4EVil/ywkWbDAtjnmbmB1zwa67lSngnlUnUYmd5s PrXt9K39hMAuCO018IUTXe4vVPHmYhG/PrFOwOUEU8g3HBSdqh/dHwWOEUxvpdGScZyoTB5D7zS 83tyQJJ7MUUQiLOoSsp/isobco+/iel2HNzQsvP6kWQce5lm6xU+bkbqVUznpnG8iDJOw74No5p 2N7ezkQjHQMDRnGRztk2af4DSKCDcmkbnR4jNNEXlndf5W1gmZfbPUaYMVxvMR6zr5qnoKIZxTJ RHdaX5GMW8OiBoolCatt8opMrCJO4KoQBNveRUiVqFSbjbaGji6x+bmiwwXpYSaIED9219lqDo/ K0sBMmaYxs4XU5BAsBbK4WvkzJ3Mg2ogFTT73hecbzW8dufyNbTI+/a+FSKOAadDTCeMB9Z5CNE J24EnaEh+gy5DyZVjWg== X-Authority-Analysis: v=2.4 cv=E/NYNqdl c=1 sm=1 tr=0 ts=6aaab172 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8 a=uDwynFsZHstSZAYALL0A:9 X-Proofpoint-ORIG-GUID: dZn6IjynXkF34tanayK0rMyapIUqzj9I X-Proofpoint-Spam-Info: AW1haW4tMjYwOTE2MDIwNCBTYWx0ZWRfXx6mlc+Tx3Q9A ubMHMxcWNFUSDmt9MM5IfmRx/bvFl5YuHFz9eyu7Tcp846T5KplXT/wyfgURHbYIOsHrEEI+jnP /f/WcmCbGMdDwx5sfSeFWegaIdttYBQ= X-Proofpoint-GUID: dZn6IjynXkF34tanayK0rMyapIUqzj9I X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-16_02,2026-09-16_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 lowpriorityscore=0 priorityscore=1501 spamscore=0 adultscore=0 clxscore=1015 bulkscore=0 malwarescore=0 suspectscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609160204 nvmet_req_find_ns() uses percpu_ref_get() to obtain a reference to the namespace. However, percpu_ref_get() can acquire a reference even after the namespace reference has been killed (or marked DEAD). This is undesirable during namespace disable because nvmet_ns_disable() kills the namespace reference and then waits for all outstanding references to drain. Acquiring a new reference after the reference is killed can therefore extend the namespace drain period. Replace percpu_ref_get() in nvmet_req_find_ns() with percpu_ref_tryget_live_rcu(), which only acquires a reference while the namespace reference is still live. This handles the race where nvmet_req_find_ns() finds ns is enabled but before it acquires the reference to ns, its reference is killed in nvmet_ns_disable(). For instnace check this race: CPU0 CPU1 nvmet_req_find_ns(): nvmet_ns_disable(): xa_load() -> ns mark == set xa_clear_mark() percpu_ref_kill() // DEAD percpu_ref_get() synchronize_rcu() | wait_for_completion() +-- succeed Replacing percpu_ref_get() with percpu_ref_tryget_live_rcu() prevents the I/O request from acquiring a namespace reference once the reference has been marked DEAD. Perform the namespace lookup and reference acquisition in nvmet_req_find_ns() within an RCU read-side critical section. nvmet_ns_disable() uses synchronize_rcu() before draining and exiting the namespace reference, ensuring that RCU readers which may be acquiring the namespace reference have completed before the reference is exited. Signed-off-by: Nilay Shroff --- drivers/nvme/target/core.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c index 77d113fceced..81a2ae072909 100644 --- a/drivers/nvme/target/core.c +++ b/drivers/nvme/target/core.c @@ -446,21 +446,27 @@ u16 nvmet_req_find_ns(struct nvmet_req *req) { u32 nsid = le32_to_cpu(req->cmd->common.nsid); struct nvmet_subsys *subsys = nvmet_req_subsys(req); + u16 status = NVME_SC_SUCCESS; + rcu_read_lock(); req->ns = xa_load(&subsys->namespaces, nsid); if (unlikely(!req->ns) || - !xa_get_mark(&subsys->namespaces, nsid, NVMET_NS_ENABLED)) { + !xa_get_mark(&subsys->namespaces, nsid, NVMET_NS_ENABLED) || + !percpu_ref_tryget_live_rcu(&req->ns->ref)) { req->error_loc = offsetof(struct nvme_common_command, nsid); - if (!req->ns) /* ns doesn't exist! */ - return NVME_SC_INVALID_NS | NVME_STATUS_DNR; + if (!req->ns) { /* ns doesn't exist! */ + status = NVME_SC_INVALID_NS | NVME_STATUS_DNR; + goto unlock; + } /* ns exists but it's disabled */ req->ns = NULL; - return NVME_SC_INTERNAL_PATH_ERROR; + status = NVME_SC_INTERNAL_PATH_ERROR; } +unlock: + rcu_read_unlock(); - percpu_ref_get(&req->ns->ref); - return NVME_SC_SUCCESS; + return status; } static void nvmet_destroy_namespace(struct percpu_ref *ref) -- 2.53.0