linux-kernel - Re: [PATCH net/tipc] Replace rcu_swap_protected() with rcu_replace

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Message-ID: <0e565b68-ece1-5ae6-bb5d-710163fb8893@windriver.com>
Date:   Tue, 10 Dec 2019 22:36:59 +0800
From:   Ying Xue <ying.xue@...driver.com>
To:     <paulmck@...nel.org>, <linux-kernel@...r.kernel.org>
CC:     <jon.maloy@...csson.com>, <davem@...emloft.net>,
        <netdev@...r.kernel.org>, <tipc-discussion@...ts.sourceforge.net>,
        <torvalds@...ux-foundation.org>, <mingo@...nel.org>,
        <kernel-team@...com>
Subject: Re: [PATCH net/tipc] Replace rcu_swap_protected() with
 rcu_replace_pointer()

On 12/10/19 11:31 AM, Paul E. McKenney wrote:
> 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>
> 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..64cf831 100644
> --- a/net/tipc/crypto.c
> +++ b/net/tipc/crypto.c
> @@ -258,7 +258,7 @@ static char *tipc_key_change_dump(struct tipc_key old, struct tipc_key new,
>  	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))
> +	rcu_replace_pointer((rcu_ptr), (ptr), lockdep_is_held(lock))

(ptr) = rcu_replace_pointer((rcu_ptr), (ptr), lockdep_is_held(lock))

>  
>  #define tipc_aead_rcu_replace(rcu_ptr, ptr, lock)			\
>  do {									\
> @@ -1189,7 +1189,7 @@ 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);

tipc_aead_rcu_swap() is only called here in TIPC module. If we use
rcu_replace_pointer() to switch pointers instead of calling
tipc_aead_rcu_swap() macro, I think we should completely remove
tipc_aead_rcu_swap().

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