netdev - Re: [tipc-discussion] [PATCH net/tipc] Replace rcu_swap_protected() with rcu_replace

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Date:   Thu, 12 Dec 2019 14:14:20 +0800
From:   Ying Xue <ying.xue@...driver.com>
To:     <paulmck@...nel.org>
CC:     Tuong Lien Tong <tuong.t.lien@...tech.com.au>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <mingo@...nel.org>, <tipc-discussion@...ts.sourceforge.net>,
        <kernel-team@...com>, <torvalds@...ux-foundation.org>,
        <davem@...emloft.net>
Subject: Re: [tipc-discussion] [PATCH net/tipc] Replace rcu_swap_protected()
 with rcu_replace_pointer()

On 12/12/19 2:46 AM, Paul E. McKenney wrote:
> On Wed, Dec 11, 2019 at 12:42:00PM +0800, Ying Xue wrote:
>> On 12/11/19 10:00 AM, Tuong Lien Tong wrote:
>>>>  
>>>>  	/* 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...
>>>
>>
>> Right. The 3rd parameter of rcu_replace_pointer() should be
>> "lockdep_is_held(&rx->lock)" instead of "&rx->lock".
> 
> Like this?

Yes, I think it's better to set the 3rd parameter of
rcu_replace_pointer() with "lockdep_is_held(&rx->lock)".

> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit 575bb4ba1b22383656760feb3d122e11656ccdfd
> Author: Paul E. McKenney <paulmck@...nel.org>
> 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+BHqta4gg6Hw@mail.gmail.com/
>     Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
>     Reported-by: kbuild test robot <lkp@...el.com>
>     Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
>     [ paulmck: Updated based on Ying Xue and Tuong Lien Tong feedback. ]
>     Cc: Jon Maloy <jon.maloy@...csson.com>
>     Cc: Ying Xue <ying.xue@...driver.com>
>     Cc: "David S. Miller" <davem@...emloft.net>
>     Cc: <netdev@...r.kernel.org>
>     Cc: <tipc-discussion@...ts.sourceforge.net>
> 
> diff --git a/net/tipc/crypto.c b/net/tipc/crypto.c
> index 990a872..c8c47fc 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, lockdep_is_held(&rx->lock));
>  		x = (key.passive - key.pending + new_pending) % KEY_MAX;
>  		new_passive = (x <= 0) ? x + KEY_MAX : x;
>  	}
>