From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH RFC 01/26] netfilter: Replace spin_unlock_wait() with lock/unlock pair Date: Thu, 29 Jun 2017 17:01:09 -0700 Message-ID: <1498780894-8253-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20170629235918.GA6445@linux.vnet.ibm.com> Cc: netfilter-devel@vger.kernel.org, netdev@vger.kernel.org, oleg@redhat.com, akpm@linux-foundation.org, mingo@redhat.com, dave@stgolabs.net, manfred@colorfullife.com, tj@kernel.org, arnd@arndb.de, linux-arch@vger.kernel.org, will.deacon@arm.com, peterz@infradead.org, stern@rowland.harvard.edu, parri.andrea@gmail.com, torvalds@linux-foundation.org, "Paul E. McKenney" , Pablo Neira Ayuso , Jozsef Kadlecsik , Florian Westphal , "David S. Miller" , To: linux-kernel@vger.kernel.org Return-path: In-Reply-To: <20170629235918.GA6445@linux.vnet.ibm.com> Sender: netdev-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org There is no agreed-upon definition of spin_unlock_wait()'s semantics, and it appears that all callers could do just as well with a lock/unlock pair. This commit therefore replaces the spin_unlock_wait() calls in nf_conntrack_lock() and nf_conntrack_all_lock() with spin_lock() followed immediately by spin_unlock(). These functions do not appear to be invoked on any fastpaths. Signed-off-by: Paul E. McKenney Cc: Pablo Neira Ayuso Cc: Jozsef Kadlecsik Cc: Florian Westphal Cc: "David S. Miller" Cc: Cc: Cc: Cc: Will Deacon Cc: Peter Zijlstra Cc: Alan Stern Cc: Andrea Parri Cc: Linus Torvalds --- net/netfilter/nf_conntrack_core.c | 26 ++++++++------------------ 1 file changed, 8 insertions(+), 18 deletions(-) diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index e847dbaa0c6b..9f997859d160 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -99,15 +99,11 @@ void nf_conntrack_lock(spinlock_t *lock) __acquires(lock) spin_lock(lock); while (unlikely(nf_conntrack_locks_all)) { spin_unlock(lock); - - /* - * Order the 'nf_conntrack_locks_all' load vs. the - * spin_unlock_wait() loads below, to ensure - * that 'nf_conntrack_locks_all_lock' is indeed held: - */ - smp_rmb(); /* spin_lock(&nf_conntrack_locks_all_lock) */ - spin_unlock_wait(&nf_conntrack_locks_all_lock); + /* Wait for nf_conntrack_locks_all_lock holder to release ... */ + spin_lock(&nf_conntrack_locks_all_lock); + spin_unlock(&nf_conntrack_locks_all_lock); spin_lock(lock); + /* ... and retry. */ } } EXPORT_SYMBOL_GPL(nf_conntrack_lock); @@ -150,17 +146,11 @@ static void nf_conntrack_all_lock(void) spin_lock(&nf_conntrack_locks_all_lock); nf_conntrack_locks_all = true; - - /* - * Order the above store of 'nf_conntrack_locks_all' against - * the spin_unlock_wait() loads below, such that if - * nf_conntrack_lock() observes 'nf_conntrack_locks_all' - * we must observe nf_conntrack_locks[] held: - */ - smp_mb(); /* spin_lock(&nf_conntrack_locks_all_lock) */ - for (i = 0; i < CONNTRACK_LOCKS; i++) { - spin_unlock_wait(&nf_conntrack_locks[i]); + /* Wait for any current holder to release lock. */ + spin_lock(&nf_conntrack_locks[i]); + spin_unlock(&nf_conntrack_locks[i]); + /* Next acquisition will see nf_conntrack_locks_all == true. */ } } -- 2.5.2