Re: [RFC] scsi: reduce protection of scan_mutex in scsi_remove_device

[Bart Van Assche <Bart.VanAssche@sandisk.com>]

On Tue, 2017-04-25 at 17:42 +0000, Song Liu wrote:
> I have been studying the code recently. I am wondering whether the following 
> would work:
> 
> 1. Introduce a new mutex for scsi_device to protect most operations in the 
>    list you gathered above;
> 
> 2. For operations like host->slave_destroy(), ensure they access scsi_host 
>    data with host_lock (or another spin lock). 
> 
>    I looked into all instances of slave_destroy, only 2 of them: 
>    dc395x_slave_destroy() and visorhba_slave_destroy() access scsi_host data 
>    without protection of spin lock. 
> 
> 3. Once 1 and 2 is ready, __scsi_remove_device() only need to hold the mutex
>    for the scsi_device. scan_mutex is no longer required. 
> 
> Is this a valid path?

Sorry but I don't think so. Unlocking and reacquiring scan_mutex would create
the potential that LUN scanning occurs in the meantime and hence that it fails
because LUN removal is incomplete.

Bart.