RE: [tipc-discussion] [PATCH net/tipc] Replace rcu_swap_protected() with rcu_replace_pointer()

[Tuong Lien Tong]

Hi Ying, Paul,

Please see my comments inline. Thanks!

BR/Tuong

-----Original Message-----
From: Ying Xue <ying.xue@xxxxxxxxxxxxx> 
Sent: Wednesday, December 11, 2019 8:32 AM
To: paulmck@xxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; mingo@xxxxxxxxxx;
tipc-discussion@xxxxxxxxxxxxxxxxxxxxx; kernel-team@xxxxxx;
torvalds@xxxxxxxxxxxxxxxxxxxx; davem@xxxxxxxxxxxxx
Subject: Re: [tipc-discussion] [PATCH net/tipc] Replace rcu_swap_protected()
with rcu_replace_pointer()

On 12/11/19 6:38 AM, Paul E. McKenney wrote:
> commit 4ee8e2c68b076867b7a5af82a38010fffcab611c
> Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Date:   Mon Dec 9 19:13:45 2019 -0800
> 
>     net/tipc: Replace rcu_swap_protected() with rcu_replace_pointer()
>     
>     This commit replaces the use of rcu_swap_protected() with the more
>     intuitively appealing rcu_replace_pointer() as a step towards removing
>     rcu_swap_protected().
>     
>     Link:
https://lore.kernel.org/lkml/CAHk-=wiAsJLw1egFEE=Z7-GGtM6wcvtyytXZA1+BHqta4g
g6Hw@xxxxxxxxxxxxxx/
>     Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>     Reported-by: kbuild test robot <lkp@xxxxxxxxx>
>     Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
>     Cc: Jon Maloy <jon.maloy@xxxxxxxxxxxx>
>     Cc: Ying Xue <ying.xue@xxxxxxxxxxxxx>
>     Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
>     Cc: <netdev@xxxxxxxxxxxxxxx>
>     Cc: <tipc-discussion@xxxxxxxxxxxxxxxxxxxxx>
> 

Acked-by: Ying Xue <ying.xue@xxxxxxxxxxxxx>

> diff --git a/net/tipc/crypto.c b/net/tipc/crypto.c
> index 990a872..978d2db 100644
> --- a/net/tipc/crypto.c
> +++ b/net/tipc/crypto.c
> @@ -257,9 +257,6 @@ static char *tipc_key_change_dump(struct tipc_key old,
struct tipc_key new,
>  #define tipc_aead_rcu_ptr(rcu_ptr, lock)				\
>  	rcu_dereference_protected((rcu_ptr), lockdep_is_held(lock))
>  
> -#define tipc_aead_rcu_swap(rcu_ptr, ptr, lock)
\
> -	rcu_swap_protected((rcu_ptr), (ptr), lockdep_is_held(lock))
> -
>  #define tipc_aead_rcu_replace(rcu_ptr, ptr, lock)			\
>  do {									\
>  	typeof(rcu_ptr) __tmp = rcu_dereference_protected((rcu_ptr),	\
> @@ -1189,7 +1186,7 @@ static bool tipc_crypto_key_try_align(struct
tipc_crypto *rx, u8 new_pending)
>  
>  	/* Move passive key if any */
>  	if (key.passive) {
> -		tipc_aead_rcu_swap(rx->aead[key.passive], tmp2, &rx->lock);
> +		tmp2 = rcu_replace_pointer(rx->aead[key.passive], tmp2,
&rx->lock);
The 3rd parameter should be the lockdep condition checking instead of the
spinlock's pointer i.e. "lockdep_is_held(&rx->lock)"?
That's why I'd prefer to use the 'tipc_aead_rcu_swap ()' macro, which is
clear & concise at least for the context here. It might be re-used later as
well...

>  		x = (key.passive - key.pending + new_pending) % KEY_MAX;
>  		new_passive = (x <= 0) ? x + KEY_MAX : x;
>  	}
> 


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