Re: Fwd: Waking up from resume locks up on sr device

[Bart Van Assche <bvanassche@acm.org>]

On 6/14/23 07:26, Alan Stern wrote:
> On Wed, Jun 14, 2023 at 04:35:50PM +0900, Damien Le Moal wrote:
>> Or... Why the heck scsi_rescan_device() is calling device_lock() ? This
>> is the only place in scsi code I can see that takes this lock. I suspect
>> this is to serialize either rescans, or serialize with resume, or both.
>> For serializing rescans, we can use another lock. For serializing with
>> PM, we should wait for PM transitions...
>> Something is not right here.
> 
> Here's what commit e27829dc92e5 ("scsi: serialize ->rescan against
> ->remove", written by Christoph Hellwig) says:
> 
>      Lock the device embedded in the scsi_device to protect against
>      concurrent calls to ->remove.
> 
> That's the commit which added the device_lock() call.

Even if scsi_rescan_device() would use another mechanism for 
serialization against sd_remove() and sr_remove(), we still need to 
solve the issue that the ATA code calls scsi_rescan_device() before 
resuming has finished. scsi_rescan_device() issues I/O. Issuing I/O to a 
device is not allowed before that device has been resumed.

Thanks,

Bart.