netdev - Re: [PATCH net-next] net-sysfs: remove possible sleep from an RCU read-side critical section

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Message-ID: <161643536180.6320.4308324155205704739@kwain.local>
Date:   Mon, 22 Mar 2021 18:49:21 +0100
From:   Antoine Tenart <atenart@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     davem@...emloft.net, kuba@...nel.org, alexander.duyck@...il.com,
        netdev@...r.kernel.org, kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH net-next] net-sysfs: remove possible sleep from an RCU read-side critical section

Quoting Matthew Wilcox (2021-03-22 18:44:21)
> On Mon, Mar 22, 2021 at 06:41:30PM +0100, Antoine Tenart wrote:
> > Quoting Matthew Wilcox (2021-03-22 17:54:39)
> > > -       rcu_read_lock();
> > > -       dev_maps = rcu_dereference(dev->xps_maps[type]);
> > > +       dev_maps = READ_ONCE(dev->xps_maps[type]);
> > 
> > Couldn't dev_maps be freed between here and the read of dev_maps->nr_ids
> > as we're not in an RCU read-side critical section?
> 
> Oh, good point.  Never mind, then.
> 
> > My feeling is there is not much value in having a tricky allocation
> > logic for reads from xps_cpus and xps_rxqs. While we could come up with
> > something, returning -ENOMEM on memory pressure should be fine.
> 
> That's fine.  It's your code, and this is probably a small allocation
> anyway.

All right. Thanks for the suggestions anyway!

Antoine