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Date:   Wed, 14 Jun 2023 11:04:55 -0700
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Subject: Re: Fwd: Waking up from resume locks up on sr device
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To:     Alan Stern <stern@rowland.harvard.edu>,
        Damien Le Moal <dlemoal@kernel.org>
Cc:     Hannes Reinecke <hare@suse.de>,
        Joe Breuer <linux-kernel@jmbreuer.net>,
        Bagas Sanjaya <bagasdotme@gmail.com>,
        Pavel Machek <pavel@ucw.cz>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <len.brown@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kees Cook <keescook@chromium.org>,
        Tony Luck <tony.luck@intel.com>,
        "Guilherme G. Piccoli" <gpiccoli@igalia.com>,
        Thorsten Leemhuis <linux@leemhuis.info>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Phillip Potter <phil@philpotter.co.uk>,
        Linux Power Management <linux-pm@vger.kernel.org>,
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        Dan Williams <dan.j.williams@intel.com>,
        Hannes Reinecke <hare@suse.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Martin Kepplinger <martin.kepplinger@puri.sm>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>
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From:   Bart Van Assche <bvanassche@acm.org>
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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.