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

[Ong, Boon Leong]

>-----Original Message-----
>From: Jose Abreu <Jose.Abreu@xxxxxxxxxxxx>
>Sent: Wednesday, January 22, 2020 5:56 PM
>To: Ong, Boon Leong <boon.leong.ong@xxxxxxxxx>; netdev@xxxxxxxxxxxxxxx
>Cc: Tan, Tee Min <tee.min.tan@xxxxxxxxx>; Voon, Weifeng
><weifeng.voon@xxxxxxxxx>; Giuseppe Cavallaro <peppe.cavallaro@xxxxxx>;
>Alexandre TORGUE <alexandre.torgue@xxxxxx>; David S . Miller
><davem@xxxxxxxxxxxxx>; Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>;
>Joao Pinto <Joao.Pinto@xxxxxxxxxxxx>; Arnd Bergmann <arnd@xxxxxxxx>;
>Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>; linux-stm32@st-md-
>mailman.stormreply.com; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
>kernel@xxxxxxxxxxxxxxx
>Subject: RE: [PATCH net v3 1/5] net: stmmac: Fix incorrect location to set
>real_num_rx|tx_queues
>
>From: Ong Boon Leong <boon.leong.ong@xxxxxxxxx>
>Date: Jan/22/2020, 09:09:32 (UTC+00:00)
>
>> For driver open(), rtnl_lock is acquired by network stack but not in the
>> resume(). Therefore, we introduce lock_acquired boolean to control when
>> to use rtnl_lock|unlock() within stmmac_hw_setup().
>
>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?