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

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Date:   Tue, 10 Dec 2019 14:38:25 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Ying Xue <ying.xue@...driver.com>
Cc:     linux-kernel@...r.kernel.org, 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 Tue, Dec 10, 2019 at 10:36:59PM +0800, Ying Xue wrote:
> 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().

Good catch, thank you!  How about the following instead?

							Thanx, Paul

------------------------------------------------------------------------

commit 4ee8e2c68b076867b7a5af82a38010fffcab611c
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>
    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..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);
 		x = (key.passive - key.pending + new_pending) % KEY_MAX;
 		new_passive = (x <= 0) ? x + KEY_MAX : x;
 	}