From: Oleg Nesterov <oleg@redhat.com>
To: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: jeremy@goop.org, kvm@vger.kernel.org, peterz@infradead.org,
virtualization@lists.linux-foundation.org,
paul.gortmaker@windriver.com, hpa@zytor.com, ak@linux.intel.com,
a.ryabinin@samsung.com, x86@kernel.org, borntraeger@de.ibm.com,
mingo@redhat.com, xen-devel@lists.xenproject.org,
paulmck@linux.vnet.ibm.com, riel@redhat.com,
konrad.wilk@oracle.com, dave@stgolabs.net,
sasha.levin@oracle.com, davej@redhat.com, tglx@linutronix.de,
waiman.long@hp.com, linux-kernel@vger.kernel.org,
pbonzini@redhat.com, akpm@linux-foundation.org,
torvalds@linux-foundation.org
Subject: Re: [PATCH V5] x86 spinlock: Fix memory corruption on completing completions
Date: Sun, 15 Feb 2015 17:17:33 +0100 [thread overview]
Message-ID: <20150215161733.GB27608@redhat.com> (raw)
In-Reply-To: <1423979744-18320-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com>
Well, I regret I mentioned the lack of barrier after enter_slowpath ;)
On 02/15, Raghavendra K T wrote:
>
> @@ -46,7 +46,8 @@ static __always_inline bool static_key_false(struct static_key *key);
>
> static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
> {
> - set_bit(0, (volatile unsigned long *)&lock->tickets.tail);
> + set_bit(0, (volatile unsigned long *)&lock->tickets.head);
> + barrier();
> }
Because this barrier() looks really confusing.
Firsty, it is equally unneeded on x86. At the same time, it can not help.
We need a memory barrier() between set_bit(SLOWPATH) and READ_ONCE(head)
to avoid the race with spin_unlock().
So I think you should replace it with smp_mb__after_atomic() or remove it.
Other than that I believe this version is correct. So I won't insist, this
is cosmetic after all.
Oleg.
next prev parent reply other threads:[~2015-02-15 16:17 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-15 5:55 [PATCH V5] x86 spinlock: Fix memory corruption on completing completions Raghavendra K T
2015-02-15 6:01 ` Raghavendra K T
2015-02-17 18:26 ` Sasha Levin
2015-02-15 16:17 ` Oleg Nesterov [this message]
2015-02-15 17:34 ` Raghavendra K T
2015-02-15 17:30 ` Raghavendra K T
2015-02-15 20:31 ` Oleg Nesterov
2015-02-16 16:47 ` [Xen-devel] " David Vrabel
2015-02-17 10:03 ` Raghavendra K T
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