Re: [PATCH -next] blk-mq: fix warning when unregister mq sysfs

[Ming Lei]

On Sat, Nov 12, 2022 at 04:28:13PM +0800, Ye Bin wrote:
> From: Ye Bin <yebin10@xxxxxxxxxx>
> 
> There's issue as follows when do fault injection test:
> ------------[ cut here ]------------
> kernfs: can not remove 'nr_tags', no directory
> WARNING: CPU: 8 PID: 2308 at fs/kernfs/dir.c:1635 kernfs_remove_by_name_ns+0xdd/0x100
> Modules linked in: null_blk(-)
> CPU: 8 PID: 2308 Comm: rmmod Not tainted 6.1.0-rc4-next-20221111+ #131
> RIP: 0010:kernfs_remove_by_name_ns+0xdd/0x100
> RSP: 0018:ffff88812149fbc8 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: ffffffffb8137508 RCX: 0000000000000000
> RDX: 0000000000000001 RSI: ffffffffb6b49ae0 RDI: ffffed1024293f6b
> RBP: ffffffffb8137600 R08: 0000000000000001 R09: ffffed1024293f3d
> R10: ffff88812149f9e7 R11: ffffed1024293f3c R12: 0000000000000000
> R13: ffffffffb6b2d2a0 R14: ffffffffb6b2d1e0 R15: ffff88822f7f14b8
> FS:  00007f97eacb9740(0000) GS:ffff8883ace00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f97e9b72b81 CR3: 000000022fbda000 CR4: 00000000000006e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  remove_files.isra.0+0x6c/0x170
>  sysfs_remove_group+0x9b/0x180
>  sysfs_remove_groups+0x4f/0xa0
>  __kobject_del+0x7d/0x1d0
>  kobject_del+0x32/0x50
>  blk_mq_sysfs_unregister.cold+0x8/0xd
>  blk_unregister_queue+0xed/0x260
>  del_gendisk+0x27e/0x900
>  null_del_dev.part.0+0x166/0x510 [null_blk]
>  null_destroy_dev+0x37/0x5c [null_blk]
>  null_exit+0x4c/0x9d [null_blk]
>  __do_sys_delete_module.isra.0+0x2f3/0x520
>  do_syscall_64+0x3b/0x90
>  entry_SYSCALL_64_after_hwframe+0x72/0xdc
>  </TASK>
> 
> 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_sysfs_register' may failed, but when unregister mq sysfs don't
> judge sysfs if registered. 'blk_mq_sysfs_register' also didn't handle
> error correctly.
> To solve above issue, if sysfs is unregstered just exit.
> 
> Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
> ---
>  block/blk-mq-sysfs.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
> index 93997d297d42..0cda0a729f3c 100644
> --- a/block/blk-mq-sysfs.c
> +++ b/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);

The above change looks fine.

>  	return ret;
>  }
>  
> @@ -278,6 +285,8 @@ void blk_mq_sysfs_unregister(struct gendisk *disk)
>  	struct blk_mq_hw_ctx *hctx;
>  	unsigned long i;
>  
> +	if (!q->mq_sysfs_init_done)
> +		return;

The above should be one warning, and I suggest to handle failure of blk_mq_sysfs_register
from blk_register_queue() in this patch too.

Thanks,
Ming