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Sun, 15 Feb 2026 13:36:23 +0000 (GMT) Message-ID: Date: Sun, 15 Feb 2026 19:06:21 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] blk-mq-debugfs: Fix warning about possible deadlock To: Mohamed Khalfella , Jens Axboe , Omar Sandoval , Ming Lei Cc: Hannes Reinecke , Yu Kuai , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260213224504.3990506-1-mkhalfella@purestorage.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20260213224504.3990506-1-mkhalfella@purestorage.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjE1MDEwOCBTYWx0ZWRfX317GoWlVQ6JG M5X0OeyJM88Cbw0jutbBu+OcOxdlBcFTLqAUBt5BfZd3UPAZQ7rq4j5XfrHh4arQaiX0RQuJrLr JIPagdXtWhq0jjK9Hcz7dyLontOd1wUQ+1y9izUorVqmkFJW3UcjmdnCYUmSvZYRRgrAOhdMAOm uTfInsf8mE3ebtpSgvhHFEGRxWy19AoINu27/U+OjP/9zUiH2J5o69Mo2g6ryShFggiyT0mkAF8 dSJ3cfzGB2ajcsWGcW5CTc47cRMUHL0PQ1zCGiDDXLE9GUs47+3W5CxqHmK0gAgFvnzX4VrSs7G FnNX5Gs9DXkJ6cqaO3NI6hmGEHbB+EDBAdj6eepL3f3ZPS802Gi5uTa93bIVMaufkuWiW37dOw7 LIyu0aFjOVhMf18clAS6NWRngMaxHZ1H3pvvdrckMPZM+s22D0v1qQktnm49WFZpp4Vl+ZbWEqH VTaha4FpIwrR8KXaXqg== X-Proofpoint-ORIG-GUID: tWl3MxVNjerv5k9vDHJ5tirmNOqSctBT X-Proofpoint-GUID: tWl3MxVNjerv5k9vDHJ5tirmNOqSctBT X-Authority-Analysis: v=2.4 cv=M7hA6iws c=1 sm=1 tr=0 ts=6991cbdd cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=HzLeVaNsDn8A:10 a=VkNPw1HP01LnGYTKEx00:22 a=Mpw57Om8IfrbqaoTuvik:22 a=GgsMoib0sEa3-_RKJdDe:22 a=VwQbUJbxAAAA:8 a=tJLSzyRPAAAA:8 a=WTJdmG3rAAAA:8 a=tIEEJtxj3QNLvETeUEAA:9 a=QEXdDO2ut3YA:10 a=H0xsmVfZzgdqH4_HIfU3:22 a=q3NGepEMMmKWaCv8Sx90:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-02-15_04,2026-02-13_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 malwarescore=0 lowpriorityscore=0 clxscore=1011 phishscore=0 impostorscore=0 suspectscore=0 priorityscore=1501 adultscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2601150000 definitions=main-2602150108 On 2/14/26 4:15 AM, Mohamed Khalfella wrote: > 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 = 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 != 0); > + WARN_ON_ONCE((q->mq_freeze_depth != 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 This issue is already being addressed here: https://lore.kernel.org/all/20260214054350.2322436-1-yukuai@fnnas.com/ Thanks, --Nilay