netdev - Re: [PATCH 5/7] ibmvnic: use a lock to serialize remove/reset

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Message-ID: <20210111114309.6de6a281@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 11 Jan 2021 11:43:09 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
Cc:     netdev@...r.kernel.org, Dany Madden <drt@...ux.ibm.com>,
        Lijun Pan <ljp@...ux.ibm.com>
Subject: Re: [PATCH 5/7] ibmvnic: use a lock to serialize remove/reset

On Sun, 10 Jan 2021 19:52:25 -0800 Sukadev Bhattiprolu wrote:
> Jakub Kicinski [kuba@...nel.org] wrote:
> > On Thu,  7 Jan 2021 23:12:34 -0800 Sukadev Bhattiprolu wrote:  
> > > Use a separate lock to serialze ibmvnic_reset() and ibmvnic_remove()
> > > functions. ibmvnic_reset() schedules work for the worker thread and
> > > ibmvnic_remove() flushes the work before removing the adapter. We
> > > don't want any work to be scheduled once we start removing the
> > > adapter (i.e after we have already flushed the work).  
> > 
> > Locking based on functions, not on data being accessed is questionable
> > IMO. If you don't want work to be scheduled isn't it enough to have a
> > bit / flag that you set to let other flows know not to schedule reset?  
> 
> Maybe I could improve the description, but the "data" being protected
> is the work queue. Basically don't add to the work queue while/after
> it is (being) flushed.
> 
> Existing code is checking for the VNIC_REMOVING state before scheduling
> the work but without a lock. If state goes to REMOVING after we check,
> we could schedule work after the flush?

I see, and you can't just use the state_lock because it has to be a
spin_lock? If that's the case please just update the commit message 
and comments to describe the data protected.