linux-kernel - [PATCH] blk-mq: check kobject state_in_sysfs before deleting in blk_mq_unregister

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Message-Id: <20250826084854.1030545-1-linan666@huaweicloud.com>
Date: Tue, 26 Aug 2025 16:48:54 +0800
From: linan666@...weicloud.com
To: axboe@...nel.dk,
	ming.lei@...hat.com,
	jianchao.w.wang@...cle.com
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linan666@...weicloud.com,
	yukuai3@...wei.com,
	yangerkun@...wei.com,
	yi.zhang@...wei.com
Subject: [PATCH] blk-mq: check kobject state_in_sysfs before deleting in blk_mq_unregister_hctx

From: Li Nan <linan122@...wei.com>

In __blk_mq_update_nr_hw_queues() the return value of
blk_mq_sysfs_register_hctxs() is not checked. If sysfs creation for hctx
fails, later changing the number of hw_queues or removing disk will
trigger the following warning:

  kernfs: can not remove 'nr_tags', no directory
  WARNING: CPU: 2 PID: 637 at fs/kernfs/dir.c:1707 kernfs_remove_by_name_ns+0x13f/0x160
  Call Trace:
   remove_files.isra.1+0x38/0xb0
   sysfs_remove_group+0x4d/0x100
   sysfs_remove_groups+0x31/0x60
   __kobject_del+0x23/0xf0
   kobject_del+0x17/0x40
   blk_mq_unregister_hctx+0x5d/0x80
   blk_mq_sysfs_unregister_hctxs+0x94/0xd0
   blk_mq_update_nr_hw_queues+0x124/0x760
   nullb_update_nr_hw_queues+0x71/0xf0 [null_blk]
   nullb_device_submit_queues_store+0x92/0x120 [null_blk]

kobjct_del() was called unconditionally even if sysfs creation failed.
Fix it by checkig the kobject creation statusbefore deleting it.

Fixes: 477e19dedc9d ("blk-mq: adjust debugfs and sysfs register when updating nr_hw_queues")
Signed-off-by: Li Nan <linan122@...wei.com>
---
 block/blk-mq-sysfs.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index 24656980f443..5c399ac562ea 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -150,9 +150,11 @@ static void blk_mq_unregister_hctx(struct blk_mq_hw_ctx *hctx)
 		return;
 
 	hctx_for_each_ctx(hctx, ctx, i)
-		kobject_del(&ctx->kobj);
+		if (ctx->kobj.state_in_sysfs)
+			kobject_del(&ctx->kobj);
 
-	kobject_del(&hctx->kobj);
+	if (hctx->kobj.state_in_sysfs)
+		kobject_del(&hctx->kobj);
 }
 
 static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx)
-- 
2.39.2