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

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Date:   Wed, 11 Dec 2019 10:46:09 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Ying Xue <ying.xue@...driver.com>
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 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?

							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;
 	}