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Fri, 13 Feb 2026 14:45:35 -0800 (PST) From: Mohamed Khalfella To: Jens Axboe , Omar Sandoval , Ming Lei Cc: Hannes Reinecke , Yu Kuai , Nilay Shroff , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Mohamed Khalfella Subject: [PATCH] blk-mq-debugfs: Fix warning about possible deadlock Date: Fri, 13 Feb 2026 14:45:04 -0800 Message-ID: <20260213224504.3990506-1-mkhalfella@purestorage.com> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Commit 65d466b62984 ("blk-mq-debugfs: warn about possible deadlock") added WARN_ONCE_ON() to debugfs_create_files() to prevent potential deadlock if the queue is frozen. We hit this warning with the stacktrace below WARNING: block/blk-mq-debugfs.c:620 at debugfs_create_files+0x9c/0x1d0 Workqueue: nvme-wq nvme_tcp_reconnect_ctrl_work [nvme_tcp] RIP: 0010:debugfs_create_files+0x9c/0x1d0 Call Trace: blk_mq_debugfs_register_hctx+0x186/0x320 blk_mq_debugfs_register_hctxs+0x80/0xa0 blk_mq_update_nr_hw_queues+0xc8f/0xd50 nvme_tcp_setup_ctrl+0xcfa/0xda0 [nvme_tcp] nvme_tcp_reconnect_ctrl_work+0x51/0x180 [nvme_tcp] process_scheduled_works+0x840/0xd80 worker_thread+0x36d/0x4a0 kthread+0x366/0x380 ret_from_fork+0x7b/0x670 ret_from_fork_asm+0x1a/0x30 Here __blk_mq_update_nr_hw_queues() did set PF_MEMALLOC_NOIO flag before calling blk_mq_debugfs_register_hctxs() and this should guarantee the described deadlock will not happen. Warn only if the queue is frozen and NOIO flag is not set. Fixes: 65d466b62984 ("blk-mq-debugfs: warn about possible deadlock") Signed-off-by: Mohamed Khalfella --- block/blk-mq-debugfs.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c index faeaa1fc86a7..ec6670dc0a3d 100644 --- a/block/blk-mq-debugfs.c +++ b/block/blk-mq-debugfs.c @@ -612,12 +612,14 @@ static void debugfs_create_files(struct request_queue= *q, struct dentry *parent, void *data, const struct blk_mq_debugfs_attr *attr) { + unsigned int pflags =3D READ_ONCE(current->flags); + lockdep_assert_held(&q->debugfs_mutex); /* * Creating new debugfs entries with queue freezed has the risk of * deadlock. */ - WARN_ON_ONCE(q->mq_freeze_depth !=3D 0); + WARN_ON_ONCE((q->mq_freeze_depth !=3D 0) && !(pflags & PF_MEMALLOC_NOIO)); /* * debugfs_mutex should not be nested under other locks that can be * grabbed while queue is frozen. base-commit: cd7a5651db263b5384aef1950898e5e889425134 --=20 2.52.0