blk-mq: fix possible memleak when register 'hctx' failed

There's issue as follows when do fault injection test:
unreferenced object 0xffff888132a9f400 (size 512):
  comm "insmod", pid 308021, jiffies 4324277909 (age 509.733s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 08 f4 a9 32 81 88 ff ff  ...........2....
    08 f4 a9 32 81 88 ff ff 00 00 00 00 00 00 00 00  ...2............
  backtrace:
    [<00000000e8952bb4>] kmalloc_node_trace+0x22/0xa0
    [<00000000f9980e0f>] blk_mq_alloc_and_init_hctx+0x3f1/0x7e0
    [<000000002e719efa>] blk_mq_realloc_hw_ctxs+0x1e6/0x230
    [<000000004f1fda40>] blk_mq_init_allocated_queue+0x27e/0x910
    [<00000000287123ec>] __blk_mq_alloc_disk+0x67/0xf0
    [<00000000a2a34657>] 0xffffffffa2ad310f
    [<00000000b173f718>] 0xffffffffa2af824a
    [<0000000095a1dabb>] do_one_initcall+0x87/0x2a0
    [<00000000f32fdf93>] do_init_module+0xdf/0x320
    [<00000000cbe8541e>] load_module+0x3006/0x3390
    [<0000000069ed1bdb>] __do_sys_finit_module+0x113/0x1b0
    [<00000000a1a29ae8>] do_syscall_64+0x35/0x80
    [<000000009cd878b0>] entry_SYSCALL_64_after_hwframe+0x46/0xb0

Fault injection context as follows:
 kobject_add
 blk_mq_register_hctx
 blk_mq_sysfs_register
 blk_register_queue
 device_add_disk
 null_add_dev.part.0 [null_blk]

As 'blk_mq_register_hctx' may already add some objects when failed halfway,
but there isn't do fallback, caller don't know which objects add failed.
To solve above issue just do fallback when add objects failed halfway in
'blk_mq_register_hctx'.
Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20221117022940.873959-1-yebin@huaweicloud.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq-sysfs.c

@@ -185,7 +185,7 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx)
 {
 	struct request_queue *q = hctx->queue;
 	struct blk_mq_ctx *ctx;
-	int i, ret;
+	int i, j, ret;
 
 	if (!hctx->nr_ctx)
 		return 0;
@@ -197,9 +197,16 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx)
 	hctx_for_each_ctx(hctx, ctx, i) {
 		ret = kobject_add(&ctx->kobj, &hctx->kobj, "cpu%u", ctx->cpu);
 		if (ret)
-			break;
+			goto out;
 	}
 
+	return 0;
+out:
+	hctx_for_each_ctx(hctx, ctx, j) {
+		if (j < i)
+			kobject_del(&ctx->kobj);
+	}
+	kobject_del(&hctx->kobj);
 	return ret;
 }