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Date:   Thu, 15 Jun 2023 06:40:15 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Damien Le Moal <dlemoal@kernel.org>
Cc:     Alan Stern <stern@rowland.harvard.edu>,
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Subject: Re: Fwd: Waking up from resume locks up on sr device
Message-ID: <20230615044015.GA4720@lst.de>
References: <5513e29d-955a-f795-21d6-ec02a2e2e128@gmail.com> <ZIQ6bkau3j6qGef8@duo.ucw.cz> <07d6e2e7-a50a-8cf4-5c5d-200551bd6687@gmail.com> <02e4f87a-80e8-dc5d-0d6e-46939f2c74ac@acm.org> <b2cf6d96-a55a-d444-d22e-e9b3945ba43f@jmbreuer.net> <84f1c51c-86f9-04b3-0cd1-f685ebee7592@kernel.org> <37ed36f0-6f72-115c-85fb-62ef5ad72e76@suse.de> <b0fdf454-b2f7-c273-66f5-efe42fbc2807@kernel.org> <859f0eda-4984-4489-9851-c9f6ec454a88@rowland.harvard.edu> <41b069c7-8723-4507-3e5a-1d1878db9002@kernel.org>
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On Thu, Jun 15, 2023 at 09:10:28AM +0900, Damien Le Moal wrote:
> > 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.
> 
> Thanks for the information.
> 
> +Christoph
> 
> Why is adding the device_lock() needed ? We could just do a
> scsi_device_get()+scsi_device_put() to serialize against remove. No ?

No.  scsi_device_get just increments a reference count, and thus
prevents ->release from beeing called.  ->remove is not in any way
affected by the refcount.