On 7/29/20 7:48 PM, Andrii Nakryiko wrote:

On Wed, Jul 29, 2020 at 7:29 AM Jakub Sitnicki [off-list ref] wrote:

quoted

On Wed, Jul 29, 2020 at 06:09 AM CEST, Andrii Nakryiko wrote:

quoted

Add test validating that all inner maps are released properly after skeleton
is destroyed. To ensure determinism, trigger kernel-side synchronize_rcu()
before checking map existence by their IDs.

Acked-by: Song Liu <redacted>
Signed-off-by: Andrii Nakryiko <redacted>

[...]

quoted

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+/*
+ * Trigger synchronize_cpu() in kernel.

Nit: synchronize_*r*cu().

welp, yeah

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+ *
+ * ARRAY_OF_MAPS/HASH_OF_MAPS lookup/update operations trigger
+ * synchronize_rcu(), if looking up/updating non-NULL element. Use this fact
+ * to trigger synchronize_cpu(): create map-in-map, create a trivial ARRAY
+ * map, update map-in-map with ARRAY inner map. Then cleanup. At the end, at
+ * least one synchronize_rcu() would be called.
+ */

That's a cool trick. I'm a bit confused by "looking up/updating non-NULL
element". It looks like you're updating an element that is NULL/unset in
the code below. What am I missing?

I was basically trying to say that it has to be a successful lookup or
update. For lookup that means looking up non-NULL (existing) entry.
For update -- setting valid inner map FD.

Not sure fixing this and typo above is worth it to post v5.

Nope, I'll fix it up while applying.