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Date:   Thu, 22 Jul 2021 21:09:43 +0800
From:   yebin <yebin10@...wei.com>
To:     <jejb@...ux.ibm.com>, <martin.petersen@...cle.com>,
        <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATH v2] scsi: scsi_dh_rdac: Avoid crash during rdac_bus_attach

On 2021/1/13 14:31, Ye Bin wrote:
> We get follow BUG_ON when rdac scan:
> [595952.944297] kernel BUG at drivers/scsi/device_handler/scsi_dh_rdac.c:427!
> [595952.951143] Internal error: Oops - BUG: 0 [#1] SMP
> ......
> [595953.251065] Call trace:
> [595953.259054]  check_ownership+0xb0/0x118
> [595953.269794]  rdac_bus_attach+0x1f0/0x4b0
> [595953.273787]  scsi_dh_handler_attach+0x3c/0xe8
> [595953.278211]  scsi_dh_add_device+0xc4/0xe8
> [595953.282291]  scsi_sysfs_add_sdev+0x8c/0x2a8
> [595953.286544]  scsi_probe_and_add_lun+0x9fc/0xd00
> [595953.291142]  __scsi_scan_target+0x598/0x630
> [595953.295395]  scsi_scan_target+0x120/0x130
> [595953.299481]  fc_user_scan+0x1a0/0x1c0 [scsi_transport_fc]
> [595953.304944]  store_scan+0xb0/0x108
> [595953.308420]  dev_attr_store+0x44/0x60
> [595953.312160]  sysfs_kf_write+0x58/0x80
> [595953.315893]  kernfs_fop_write+0xe8/0x1f0
> [595953.319888]  __vfs_write+0x60/0x190
> [595953.323448]  vfs_write+0xac/0x1c0
> [595953.326836]  ksys_write+0x74/0xf0
> [595953.330221]  __arm64_sys_write+0x24/0x30
>
> BUG_ON code is in check_ownership:
>                  list_for_each_entry_rcu(tmp, &h->ctlr->dh_list, node) {
>                          /* h->sdev should always be valid */
>                          BUG_ON(!tmp->sdev);
>                          tmp->sdev->access_state = access_state;
>                  }
> rdac_bus_attach
> 	initialize_controller
> 		list_add_rcu(&h->node, &h->ctlr->dh_list);
> 		h->sdev = sdev;
> rdac_bus_detach
> 	list_del_rcu(&h->node);
> 	h->sdev = NULL;
>
> Test as follow steps:
> (1) Find IO error, remove disk;
> (2) Insert disk back;
> (3) trigger scan disk;
>
> There is race between rdac_bus_attach and rdac_bus_detach, maybe access
> rdac_dh_data which h->sdev has been set NULL when process rdac attach. And also
> find that "h->sdev" set value after add list, this may lead to reference NULL ptr.
>
> Signed-off-by: Ye Bin <yebin10@...wei.com>
> ---
>   drivers/scsi/device_handler/scsi_dh_rdac.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/device_handler/scsi_dh_rdac.c b/drivers/scsi/device_handler/scsi_dh_rdac.c
> index 5efc959493ec..85a71bafaea7 100644
> --- a/drivers/scsi/device_handler/scsi_dh_rdac.c
> +++ b/drivers/scsi/device_handler/scsi_dh_rdac.c
> @@ -453,8 +453,8 @@ static int initialize_controller(struct scsi_device *sdev,
>   		if (!h->ctlr)
>   			err = SCSI_DH_RES_TEMP_UNAVAIL;
>   		else {
> -			list_add_rcu(&h->node, &h->ctlr->dh_list);
>   			h->sdev = sdev;
> +			list_add_rcu(&h->node, &h->ctlr->dh_list);
>   		}
>   		spin_unlock(&list_lock);
>   		err = SCSI_DH_OK;
> @@ -778,11 +778,11 @@ static void rdac_bus_detach( struct scsi_device *sdev )
>   	spin_lock(&list_lock);
>   	if (h->ctlr) {
>   		list_del_rcu(&h->node);
> -		h->sdev = NULL;
>   		kref_put(&h->ctlr->kref, release_controller);
>   	}
>   	spin_unlock(&list_lock);
>   	sdev->handler_data = NULL;
> +	synchronize_rcu();
>   	kfree(h);
>   }
>   
ping ...

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