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)

quoted

-       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.