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 V3] x86 spinlock: Fix memory corruption on completing completions
Date: Thu, 12 Feb 2015 14:50:56 +0100 [thread overview]
Message-ID: <20150212135056.GA10646@redhat.com> (raw)
In-Reply-To: <1423741647-2156-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com>
On 02/12, Raghavendra K T wrote:
>
> @@ -191,8 +189,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
> * We need to check "unlocked" in a loop, tmp.head == head
> * can be false positive because of overflow.
> */
> - if (tmp.head == (tmp.tail & ~TICKET_SLOWPATH_FLAG) ||
> - tmp.head != head)
> + if (__tickets_equal(tmp.head, tmp.tail) || tmp.head != head)
> break;
Ah, it seems that "tmp.head != head" should be turned into
!__tickets_equal(), no?
Suppose that TICKET_SLOWPATH_FLAG is set after the first ACCESS_ONCE(head),
then tmp.head != head will be true before the first unlock we are waiting
for.
And perhaps you can turn these ACCESS_ONCE into READ_ONCE as well.
Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg@redhat.com>
To: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
peterz@infradead.org, torvalds@linux-foundation.org,
konrad.wilk@oracle.com, pbonzini@redhat.com,
paulmck@linux.vnet.ibm.com, waiman.long@hp.com, davej@redhat.com,
x86@kernel.org, jeremy@goop.org, paul.gortmaker@windriver.com,
ak@linux.intel.com, jasowang@redhat.com,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
virtualization@lists.linux-foundation.org,
xen-devel@lists.xenproject.org, riel@redhat.com,
borntraeger@de.ibm.com, akpm@linux-foundation.org,
a.ryabinin@samsung.com, sasha.levin@oracle.com,
dave@stgolabs.net
Subject: Re: [PATCH V3] x86 spinlock: Fix memory corruption on completing completions
Date: Thu, 12 Feb 2015 14:50:56 +0100 [thread overview]
Message-ID: <20150212135056.GA10646@redhat.com> (raw)
In-Reply-To: <1423741647-2156-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com>
On 02/12, Raghavendra K T wrote:
>
> @@ -191,8 +189,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
> * We need to check "unlocked" in a loop, tmp.head == head
> * can be false positive because of overflow.
> */
> - if (tmp.head == (tmp.tail & ~TICKET_SLOWPATH_FLAG) ||
> - tmp.head != head)
> + if (__tickets_equal(tmp.head, tmp.tail) || tmp.head != head)
> break;
Ah, it seems that "tmp.head != head" should be turned into
!__tickets_equal(), no?
Suppose that TICKET_SLOWPATH_FLAG is set after the first ACCESS_ONCE(head),
then tmp.head != head will be true before the first unlock we are waiting
for.
And perhaps you can turn these ACCESS_ONCE into READ_ONCE as well.
Oleg.
next prev parent reply other threads:[~2015-02-12 13:50 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-12 11:47 [PATCH V3] x86 spinlock: Fix memory corruption on completing completions Raghavendra K T
2015-02-12 11:47 ` Raghavendra K T
2015-02-12 11:47 ` Raghavendra K T
2015-02-12 13:37 ` Oleg Nesterov
2015-02-12 13:37 ` Oleg Nesterov
2015-02-12 14:21 ` Raghavendra K T
2015-02-12 14:21 ` Raghavendra K T
2015-02-12 14:21 ` Raghavendra K T
2015-02-12 13:37 ` Oleg Nesterov
2015-02-12 13:50 ` Oleg Nesterov
2015-02-12 13:50 ` Oleg Nesterov [this message]
2015-02-12 13:50 ` Oleg Nesterov
2015-02-12 14:23 ` Raghavendra K T
2015-02-12 14:23 ` Raghavendra K T
2015-02-12 14:23 ` Raghavendra K T
2015-02-12 14:02 ` Oleg Nesterov
2015-02-12 14:02 ` Oleg Nesterov
2015-02-12 14:25 ` Raghavendra K T
2015-02-12 14:25 ` Raghavendra K T
2015-02-12 14:25 ` Raghavendra K T
2015-02-12 14:02 ` Oleg Nesterov
2015-02-12 15:00 ` Peter Zijlstra
2015-02-12 15:00 ` Peter Zijlstra
2015-02-12 15:28 ` Raghavendra K T
2015-02-12 15:28 ` Raghavendra K T
2015-02-12 15:28 ` Raghavendra K T
2015-02-12 15:00 ` Peter Zijlstra
-- strict thread matches above, loose matches on Subject: below --
2015-02-12 11:47 Raghavendra K T
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