From: Will Deacon <will.deacon@arm.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.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,
manfred@colorfullife.com, tj@kernel.org, arnd@arndb.de,
linux-arch@vger.kernel.org, peterz@infradead.org,
stern@rowland.harvard.edu, parri.andrea@gmail.com,
torvalds@linux-foundation.org
Subject: Re: [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic definitions
Date: Fri, 30 Jun 2017 14:13:39 +0100 [thread overview]
Message-ID: <20170630131339.GA14118@arm.com> (raw)
In-Reply-To: <20170630123815.GT2393@linux.vnet.ibm.com>
On Fri, Jun 30, 2017 at 05:38:15AM -0700, Paul E. McKenney wrote:
> On Fri, Jun 30, 2017 at 10:19:29AM +0100, Will Deacon wrote:
> > On Thu, Jun 29, 2017 at 05:01:16PM -0700, 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 removes spin_unlock_wait() and related
> > > definitions from core code.
> > >
> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > Cc: Arnd Bergmann <arnd@arndb.de>
> > > Cc: Ingo Molnar <mingo@redhat.com>
> > > 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>
> > > ---
> > > include/asm-generic/qspinlock.h | 14 -----
> > > include/linux/spinlock.h | 31 -----------
> > > include/linux/spinlock_up.h | 6 ---
> > > kernel/locking/qspinlock.c | 117 ----------------------------------------
> > > 4 files changed, 168 deletions(-)
> >
> > [...]
> >
> > > diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
> > > index b2caec7315af..64a9051e4c2c 100644
> > > --- a/kernel/locking/qspinlock.c
> > > +++ b/kernel/locking/qspinlock.c
> > > @@ -267,123 +267,6 @@ static __always_inline u32 __pv_wait_head_or_lock(struct qspinlock *lock,
> > > #define queued_spin_lock_slowpath native_queued_spin_lock_slowpath
> > > #endif
> > >
> > > -/*
> > > - * Various notes on spin_is_locked() and spin_unlock_wait(), which are
> > > - * 'interesting' functions:
> > > - *
> > > - * PROBLEM: some architectures have an interesting issue with atomic ACQUIRE
> > > - * operations in that the ACQUIRE applies to the LOAD _not_ the STORE (ARM64,
> > > - * PPC). Also qspinlock has a similar issue per construction, the setting of
> > > - * the locked byte can be unordered acquiring the lock proper.
> > > - *
> > > - * This gets to be 'interesting' in the following cases, where the /should/s
> > > - * end up false because of this issue.
> > > - *
> > > - *
> > > - * CASE 1:
> > > - *
> > > - * So the spin_is_locked() correctness issue comes from something like:
> > > - *
> > > - * CPU0 CPU1
> > > - *
> > > - * global_lock(); local_lock(i)
> > > - * spin_lock(&G) spin_lock(&L[i])
> > > - * for (i) if (!spin_is_locked(&G)) {
> > > - * spin_unlock_wait(&L[i]); smp_acquire__after_ctrl_dep();
> > > - * return;
> > > - * }
> > > - * // deal with fail
> > > - *
> > > - * Where it is important CPU1 sees G locked or CPU0 sees L[i] locked such
> > > - * that there is exclusion between the two critical sections.
> > > - *
> > > - * The load from spin_is_locked(&G) /should/ be constrained by the ACQUIRE from
> > > - * spin_lock(&L[i]), and similarly the load(s) from spin_unlock_wait(&L[i])
> > > - * /should/ be constrained by the ACQUIRE from spin_lock(&G).
> > > - *
> > > - * Similarly, later stuff is constrained by the ACQUIRE from CTRL+RMB.
> >
> > Might be worth keeping this comment about spin_is_locked, since we're not
> > removing that guy just yet!
>
> Ah, all the examples had spin_unlock_wait() in them. So what I need to
> do is to create a spin_unlock_wait()-free example to illustrate the
> text starting with "The load from spin_is_locked(", correct?
Yeah, I think so.
> I also need to check all uses of spin_is_locked(). There might no
> longer be any that rely on any particular ordering...
Right. I think we're looking for the "insane case" as per 38b850a73034
(which was apparently used by ipc/sem.c at the time, but no longer).
There's a usage in kernel/debug/debug_core.c, but it doesn't fill me with
joy.
Will
next prev parent reply other threads:[~2017-06-30 13:13 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
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 [this message]
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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