netdev - Re: [PATCH net v2 2/6] netdevsim: disable devlink reload when resources are being used

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Message-ID: <20200201092320.10a3381b@cakuba.hsd1.ca.comcast.net>
Date:   Sat, 1 Feb 2020 09:23:20 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Taehee Yoo <ap420073@...il.com>
Cc:     David Miller <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net v2 2/6] netdevsim: disable devlink reload when
 resources are being used

On Sat, 1 Feb 2020 18:37:58 +0900, Taehee Yoo wrote:
> > > +     mutex_lock(&nsim_bus_dev_ops_lock);  
> >
> > Not sure why we have to lock the big lock here?
> 
> The reason for using this lock is to protect "nsim_dev".
> nsim_dev_take_snapshot_write() uses nsim_dev.
> So if nsim_dev is removed while this function is being used,
> panic will occur.
> nsim_dev is protected by nsim_bus_dev_ops_lock.
> So, this lock should be used.

I see.

> But, I found deadlock because of this lock.
> Structurally, this lock couldn't be used in snapshot_write().
> So, I will find another way.

Could we perhaps use the lock in struct device? Seems like it would 
be a good fit for protecting nsim_dev?