From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: linux-kernel@vger.kernel.org, netfilter-devel@vger.kernel.org,
netdev@vger.kernel.org, oleg@redhat.com,
akpm@linux-foundation.org, mingo@redhat.com, dave@stgolabs.net,
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,
Pablo Neira Ayuso <pablo@netfilter.org>,
Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>,
Florian Westphal <fw@strlen.de>,
"David S. Miller" <davem@davemloft.net>,
coreteam@netfilter.org
Subject: Re: [PATCH RFC 01/26] netfilter: Replace spin_unlock_wait() with lock/unlock pair
Date: Sat, 1 Jul 2017 19:00:45 -0700 [thread overview]
Message-ID: <20170702020045.GR2393@linux.vnet.ibm.com> (raw)
In-Reply-To: <a6642feb-2f3a-980f-5ed6-2deb79563e6b@colorfullife.com>
On Sat, Jul 01, 2017 at 09:44:12PM +0200, Manfred Spraul wrote:
> Hi Paul,
>
> On 06/30/2017 02:01 AM, Paul E. McKenney wrote:
> >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<paulmck@linux.vnet.ibm.com>
> >Cc: Pablo Neira Ayuso<pablo@netfilter.org>
> >Cc: Jozsef Kadlecsik<kadlec@blackhole.kfki.hu>
> >Cc: Florian Westphal<fw@strlen.de>
> >Cc: "David S. Miller"<davem@davemloft.net>
> >Cc:<netfilter-devel@vger.kernel.org>
> >Cc:<coreteam@netfilter.org>
> >Cc:<netdev@vger.kernel.org>
> >Cc: Will Deacon<will.deacon@arm.com>
> >Cc: Peter Zijlstra<peterz@infradead.org>
> >Cc: Alan Stern<stern@rowland.harvard.edu>
> >Cc: Andrea Parri<parri.andrea@gmail.com>
> >Cc: Linus Torvalds<torvalds@linux-foundation.org>
> >---
> > 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)) {
> I think here an ACQUIRE is missing.
> > 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. */
> > }
> > }
> As far as I see, nf_conntrack_locks[] nests inside
> nf_conntrack_lock_all_lock.
> So
> spin_lock(&nf_conntrack_locks_all_lock);
> spin_lock(lock);
> spin_unlock(&nf_conntrack_locks_all_lock);
>
> can replace the retry logic.
>
> Correct? Then what about the attached patch?
At first glance, it looks correct to me, thank you! I have replaced my
patch with this one for testing and further review.
Thanx, Paul
> --
> Manfred
>
>
> >From 453e7a77f3756d939c754031b092cbdfbd149559 Mon Sep 17 00:00:00 2001
> From: Manfred Spraul <manfred@colorfullife.com>
> Date: Sun, 21 Aug 2016 07:17:55 +0200
> Subject: [PATCH] net/netfilter/nf_conntrack_core: Fix net_conntrack_lock()
>
> As we want to remove spin_unlock_wait() and replace it with explicit
> spin_lock()/spin_unlock() calls, we can use this to simplify the
> locking.
>
> In addition:
> - Reading nf_conntrack_locks_all needs ACQUIRE memory ordering.
> - The new code avoids the backwards loop.
>
> Only slightly tested, I did not manage to trigger calls to
> nf_conntrack_all_lock().
>
> Fixes: b16c29191dc8
> Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
> Cc: <stable@vger.kernel.org>
> Cc: Sasha Levin <sasha.levin@oracle.com>
> Cc: Pablo Neira Ayuso <pablo@netfilter.org>
> Cc: netfilter-devel@vger.kernel.org
> ---
> net/netfilter/nf_conntrack_core.c | 44 +++++++++++++++++++++------------------
> 1 file changed, 24 insertions(+), 20 deletions(-)
>
> diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
> index e847dba..1193565 100644
> --- a/net/netfilter/nf_conntrack_core.c
> +++ b/net/netfilter/nf_conntrack_core.c
> @@ -96,19 +96,24 @@ static struct conntrack_gc_work conntrack_gc_work;
>
> void nf_conntrack_lock(spinlock_t *lock) __acquires(lock)
> {
> + /* 1) Acquire the 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);
> - spin_lock(lock);
> - }
> + /* 2) read nf_conntrack_locks_all, with ACQUIRE semantics */
> + if (likely(smp_load_acquire(&nf_conntrack_locks_all) == false))
> + return;
> +
> + /* fast path failed, unlock */
> + spin_unlock(lock);
> +
> + /* Slow path 1) get global lock */
> + spin_lock(&nf_conntrack_locks_all_lock);
> +
> + /* Slow path 2) get the lock we want */
> + spin_lock(lock);
> +
> + /* Slow path 3) release the global lock */
> + spin_unlock(&nf_conntrack_locks_all_lock);
> }
> EXPORT_SYMBOL_GPL(nf_conntrack_lock);
>
> @@ -149,18 +154,17 @@ static void nf_conntrack_all_lock(void)
> int i;
>
> 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) */
> + nf_conntrack_locks_all = true;
>
> for (i = 0; i < CONNTRACK_LOCKS; i++) {
> - spin_unlock_wait(&nf_conntrack_locks[i]);
> + spin_lock(&nf_conntrack_locks[i]);
> +
> + /* This spin_unlock provides the "release" to ensure that
> + * nf_conntrack_locks_all==true is visible to everyone that
> + * acquired spin_lock(&nf_conntrack_locks[]).
> + */
> + spin_unlock(&nf_conntrack_locks[i]);
> }
> }
>
> --
> 2.9.4
>
next prev parent reply other threads:[~2017-07-02 2:00 UTC|newest]
Thread overview: 122+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-29 23:59 [PATCH RFC 0/26] Remove spin_unlock_wait() Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 01/26] netfilter: Replace spin_unlock_wait() with lock/unlock pair Paul E. McKenney
[not found] ` <a6642feb-2f3a-980f-5ed6-2deb79563e6b@colorfullife.com>
2017-07-02 2:00 ` Paul E. McKenney [this message]
2017-07-03 14:39 ` Alan Stern
2017-07-03 17:14 ` Paul E. McKenney
2017-07-03 19:01 ` Manfred Spraul
2017-07-03 19:57 ` Alan Stern
2017-07-06 18:43 ` Manfred Spraul
2017-07-03 20:04 ` Alan Stern
2017-07-03 20:53 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 02/26] task_work: " Paul E. McKenney
2017-06-30 11:04 ` Oleg Nesterov
2017-06-30 12:50 ` Paul E. McKenney
2017-06-30 15:20 ` Oleg Nesterov
2017-06-30 16:16 ` Paul E. McKenney
2017-06-30 17:21 ` Paul E. McKenney
2017-06-30 19:21 ` Oleg Nesterov
2017-06-30 19:50 ` Alan Stern
2017-06-30 20:04 ` Paul E. McKenney
2017-06-30 20:02 ` Paul E. McKenney
2017-06-30 20:19 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 03/26] sched: " Paul E. McKenney
2017-06-30 10:31 ` Arnd Bergmann
2017-06-30 12:35 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 04/26] completion: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 05/26] exit: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 07/26] drivers/ata: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic definitions Paul E. McKenney
2017-06-30 9:19 ` Will Deacon
2017-06-30 12:38 ` Paul E. McKenney
2017-06-30 13:13 ` Will Deacon
2017-06-30 22:18 ` Paul E. McKenney
2017-07-03 13:15 ` Will Deacon
2017-07-03 16:18 ` Paul E. McKenney
2017-07-03 16:40 ` Linus Torvalds
2017-07-03 17:13 ` Will Deacon
2017-07-03 22:30 ` Paul E. McKenney
2017-07-03 22:49 ` Linus Torvalds
2017-07-04 0:39 ` Paul E. McKenney
2017-07-04 0:54 ` Paul E. McKenney
2017-07-03 21:10 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 09/26] alpha: Remove spin_unlock_wait() arch-specific definitions Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 10/26] arc: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 11/26] arm: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 12/26] arm64: " Paul E. McKenney
2017-06-30 9:20 ` Will Deacon
2017-06-30 17:29 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 13/26] blackfin: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 14/26] hexagon: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 15/26] ia64: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 16/26] m32r: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 18/26] mips: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 19/26] mn10300: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 20/26] parisc: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 21/26] powerpc: " Paul E. McKenney
2017-07-02 3:58 ` Boqun Feng
2017-07-05 23:57 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 22/26] s390: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 23/26] sh: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 24/26] sparc: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 25/26] tile: " Paul E. McKenney
2017-06-30 0:06 ` Linus Torvalds
2017-06-30 0:09 ` Paul E. McKenney
2017-06-30 0:14 ` Paul E. McKenney
2017-06-30 0:10 ` Linus Torvalds
2017-06-30 0:24 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 26/26] xtensa: " Paul E. McKenney
[not found] ` <1498780894-8253-6-git-send-email-paulmck@linux.vnet.ibm.com>
2017-07-01 19:23 ` [PATCH RFC 06/26] ipc: Replace spin_unlock_wait() with lock/unlock pair Manfred Spraul
2017-07-02 3:16 ` Paul E. McKenney
2017-07-05 23:29 ` [PATCH v2 0/9] Remove spin_unlock_wait() Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 1/9] net/netfilter/nf_conntrack_core: Fix net_conntrack_lock() Paul E. McKenney
2017-07-06 18:45 ` Manfred Spraul
2017-07-06 20:26 ` Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 2/9] task_work: Replace spin_unlock_wait() with lock/unlock pair Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 3/9] sched: " Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 4/9] completion: " Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 5/9] exit: " Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 6/9] ipc: " Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 7/9] drivers/ata: " Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 8/9] locking: Remove spin_unlock_wait() generic definitions Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 9/9] arch: Remove spin_unlock_wait() arch-specific definitions Paul E. McKenney
2017-07-06 14:12 ` [PATCH v2 0/9] Remove spin_unlock_wait() David Laight
2017-07-06 15:21 ` Paul E. McKenney
2017-07-06 16:10 ` Peter Zijlstra
2017-07-06 16:24 ` Paul E. McKenney
2017-07-06 16:41 ` Peter Zijlstra
2017-07-06 17:03 ` Paul E. McKenney
2017-07-06 16:49 ` Alan Stern
2017-07-06 16:54 ` Peter Zijlstra
2017-07-06 19:37 ` Alan Stern
2017-07-06 16:05 ` Peter Zijlstra
2017-07-06 16:20 ` Paul E. McKenney
2017-07-06 16:50 ` Peter Zijlstra
2017-07-06 17:08 ` Will Deacon
2017-07-06 17:29 ` Paul E. McKenney
2017-07-06 17:18 ` Paul E. McKenney
2017-07-07 8:31 ` Ingo Molnar
2017-07-07 8:44 ` Peter Zijlstra
2017-07-07 10:33 ` Ingo Molnar
2017-07-07 11:23 ` Peter Zijlstra
2017-07-07 14:41 ` Paul E. McKenney
2017-07-08 8:43 ` Ingo Molnar
2017-07-08 11:41 ` Paul E. McKenney
2017-07-07 17:47 ` Manfred Spraul
2017-07-08 8:35 ` Ingo Molnar
2017-07-08 11:39 ` Paul E. McKenney
2017-07-08 12:30 ` Ingo Molnar
2017-07-08 14:45 ` Paul E. McKenney
2017-07-08 16:21 ` Alan Stern
2017-07-10 17:22 ` Manfred Spraul
2017-07-07 8:06 ` Ingo Molnar
2017-07-07 9:32 ` Ingo Molnar
2017-07-07 19:27 ` [PATCH v3 " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 1/9] net/netfilter/nf_conntrack_core: Fix net_conntrack_lock() Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 2/9] task_work: Replace spin_unlock_wait() with lock/unlock pair Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 3/9] sched: " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 4/9] completion: " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 5/9] exit: " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 6/9] ipc: " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 7/9] drivers/ata: " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 8/9] locking: Remove spin_unlock_wait() generic definitions Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 9/9] arch: Remove spin_unlock_wait() arch-specific definitions Paul E. McKenney
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