RE: [PATCH net v3 1/5] net: stmmac: Fix incorrect location to set real_num_rx|tx_queues

From: Ong, Boon Leong <redacted>
Date: Jan/24/2020, 08:56:28 (UTC+00:00)

quoted

Why not use rtnl_is_locked() instead of the boolean ?

We know that stmmac_open() is called with rtnl_mutex locked by caller.
And, stmmac_resume() is called without rtnl_mutex is locked by caller.
If we replace the boolean with rtnl_is_locked(), then we will have the
following logics in stmmac_hw_setup():-

     if (!rtnl_is_locked)   ---- (A)
         rtnl_lock();
     netif_set_real_num_rx_queues();
     netif_set_real_num_tx_queues();
     if (!rtnl_is_locked)   ---- (B)
         rtnl_unlock();

For stmmac_open(), (A) is false but (B) is true. 
So, the stmmac_open() exits with rtnl_mutex is released.
Here, the above logic does not perserve the original rtnl_mutex
is locked when stmmac_open() is called.

For stmmac_resume(), (A) is true, and (B) is also true.
So, the stmmac_resume() exits with rtnl_mutex is released.
Here, the above logic works well as the original rtnl_mutex is released
when stmmac_resume() is called.
 
So, as far as I can see, the proposed boolean approach works fine for both
stmmac_open() and stmmac_resume().

Do you agree? 

Can't you just wrap all the HW related logic in stmmac_resume() and 
stmmac_suspend() with the rtnl lock ? Seems like the right thing to do and 
you won't need the boolean.

---
Thanks,
Jose Miguel Abreu

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