linux-kernel - Re: [PATCH] scsi: scsi_dh_rdac: Avoid crash when a disk attach failed

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Date:   Wed, 6 Sep 2023 10:51:04 -0500
From:   Mike Christie <michael.christie@...cle.com>
To:     Huang Cun <huangcun@...gfor.com.cn>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     dinghui@...gfor.com.cn, pengdonglin@...gfor.com.cn
Subject: Re: [PATCH] scsi: scsi_dh_rdac: Avoid crash when a disk attach failed

On 8/3/23 6:28 AM, Huang Cun wrote:
> When a disk fails to attach, the struct rdac_dh_data is released,
> but it is not removed from the ctlr->dh_list. When attaching another
> disk, the released rdac_dh_data will be accessed and the following
> BUG_ON() may be observed:
> 
> [  414.696167] scsi 5:0:0:7: rdac: Attach failed (8)
> ...
> [  423.615364] kernel BUG at drivers/scsi/device_handler/scsi_dh_rdac.c:427!
> [  423.615731] invalid opcode: 0000 [#1] SMP NOPTI
> ...
> [  423.623247] Call Trace:
> [  423.623598]  rdac_bus_attach+0x203/0x4c0
> [  423.623949]  ? scsi_dh_handler_attach+0x2d/0x90
> [  423.624300]  scsi_dh_handler_attach+0x2d/0x90
> [  423.624652]  scsi_sysfs_add_sdev+0x88/0x270
> [  423.625004]  scsi_probe_and_add_lun+0xc47/0xd50
> [  423.625354]  scsi_report_lun_scan+0x339/0x3b0
> [  423.625705]  __scsi_scan_target+0xe9/0x220
> [  423.626056]  scsi_scan_target+0xf6/0x100
> [  423.626404]  fc_scsi_scan_rport+0xa5/0xb0
> [  423.626757]  process_one_work+0x15e/0x3f0
> [  423.627106]  worker_thread+0x4c/0x440
> [  423.627453]  ? rescuer_thread+0x350/0x350
> [  423.627804]  kthread+0xf8/0x130
> [  423.628153]  ? kthread_destroy_worker+0x40/0x40
> [  423.628509]  ret_from_fork+0x1f/0x40
> 
> Fixes: 1a5dc166cd88 ("scsi_dh_rdac: update 'access_state' field")
> Signed-off-by: Huang Cun <huangcun@...gfor.com.cn>
> Signed-off-by: Ding Hui <dinghui@...gfor.com.cn>
> Cc: Donglin Peng <pengdonglin@...gfor.com.cn>
> ---
>  drivers/scsi/device_handler/scsi_dh_rdac.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/scsi/device_handler/scsi_dh_rdac.c b/drivers/scsi/device_handler/scsi_dh_rdac.c
> index c5538645057a..9d487c2b7708 100644
> --- a/drivers/scsi/device_handler/scsi_dh_rdac.c
> +++ b/drivers/scsi/device_handler/scsi_dh_rdac.c
> @@ -762,8 +762,10 @@ static int rdac_bus_attach(struct scsi_device *sdev)
>  
>  clean_ctlr:
>  	spin_lock(&list_lock);
> +	list_del_rcu(&h->node);
>  	kref_put(&h->ctlr->kref, release_controller);
>  	spin_unlock(&list_lock);
> +	synchronize_rcu();
>  

Should this be:

spin_lock(&list_lock);
list_del_rcu(&h->node);
spin_unlock(&list_lock);

synchronize_rcu();

kref_put(&h->ctlr->kref, release_controller);


?

If you do the synchronize_rcu after the kref_put, then the kref_put
could free the rdac_dh_data, while check_ownership is still
accessing the rdac_dh_data, right?