Re: [PATCH 4/8] iwlwifi: mvm: fix race in sync rx queue notification

[Kalle Valo <kvalo@codeaurora.org>]

Luca Coelho <luca@coelho.fi> writes:

> From: Naftali Goldstein <naftali.goldstein@intel.com>
>
> Consider the following flow:
>  1. Driver starts to sync the rx queues due to a delba.
>     mvm->queue_sync_cookie=1.
>     This rx-queues-sync is synchronous, so it doesn't increment the
>     cookie until all rx queues handle the notification from FW.
>  2. During this time, driver starts to sync rx queues due to nssn sync
>     required.
>     The cookie's value is still 1, but it doesn't matter since this
>     rx-queue-sync is non-synchronous so in the notification handler the
>     cookie is ignored.
>     What _does_ matter is that this flow increments the cookie to 2
>     immediately.
>     Remember though that the FW won't start servicing this command until
>     it's done with the previous one.
>  3. FW is still handling the first command, so it sends a notification
>     with internal_notif->sync=1, and internal_notif->cookie=0, which
>     triggers a WARN_ONCE.
>
> The solution for this race is to only use the mvm->queue_sync_cookie in
> case of a synchronous sync-rx-queues. This way in step 2 the cookie's
> value won't change so we avoid the WARN.
>
> The commit in the "fixes" field is the first commit to introduce
> non-synchronous sending of this command to FW.

But I don't see a Fixes field anywhere :)

-- 
Kalle Valo