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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20210322174421.GT1719932@casper.infradead.org>
Date:   Mon, 22 Mar 2021 17:44:21 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Antoine Tenart <atenart@...nel.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

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.