From: "Jan Beulich" <JBeulich@suse.com>
To: "Juergen Gross" <jgross@suse.com>
Cc: "Borislav Petkov" <bp@alien8.de>,
"Peter Zijlstra" <peterz@infradead.org>,
"the arch/x86 maintainers" <x86@kernel.org>, <tglx@linutronix.de>,
"xen-devel" <xen-devel@lists.xenproject.org>,
"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
<longman@redhat.com>, <mingo@redhat.com>,
<linux-kernel@vger.kernel.org>, <stable@vger.kernel.org>,
<hpa@zytor.com>
Subject: Re: [Xen-devel] [PATCH 1/2] xen: fix race in xen_qlock_wait()
Date: Mon, 01 Oct 2018 02:54:13 -0600 [thread overview]
Message-ID: <5BB1E0B502000078001ED124@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <20181001071641.19282-2-jgross@suse.com>
>>> On 01.10.18 at 09:16, <jgross@suse.com> wrote:
> In the following situation a vcpu waiting for a lock might not be
> woken up from xen_poll_irq():
>
> CPU 1: CPU 2: CPU 3:
> takes a spinlock
> tries to get lock
> -> xen_qlock_wait()
> -> xen_clear_irq_pending()
Doesn't the last line above ...
> frees the lock
> -> xen_qlock_kick(cpu2)
... need to be below here?
> takes lock again
> tries to get lock
> -> *lock = _Q_SLOW_VAL
> -> *lock == _Q_SLOW_VAL ?
> -> xen_poll_irq()
> frees the lock
> -> xen_qlock_kick(cpu3)
>
> And cpu 2 will sleep forever.
>
> This can be avoided easily by modifying xen_qlock_wait() to call
> xen_poll_irq() only if the related irq was not pending and to call
> xen_clear_irq_pending() only if it was pending.
>
> Cc: stable@vger.kernel.org
> Cc: Waiman.Long@hp.com
> Cc: peterz@infradead.org
> Signed-off-by: Juergen Gross <jgross@suse.com>
Patch itself
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Jan
next prev parent reply other threads:[~2018-10-01 8:54 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-01 7:16 [PATCH 0/2] xen: fix two issues in Xen pv qspinlock handling Juergen Gross
2018-10-01 7:16 ` [PATCH 1/2] xen: fix race in xen_qlock_wait() Juergen Gross
2018-10-01 7:37 ` Juergen Gross
2018-10-01 7:37 ` Juergen Gross
2018-10-01 8:54 ` Jan Beulich
2018-10-01 8:54 ` Jan Beulich [this message]
2018-10-01 7:16 ` Juergen Gross
2018-10-01 7:16 ` [PATCH 2/2] xen: make xen_qlock_wait() nestable Juergen Gross
2018-10-01 7:16 ` Juergen Gross
2018-10-01 7:38 ` Juergen Gross
2018-10-01 7:38 ` Juergen Gross
2018-10-01 8:57 ` Jan Beulich
2018-10-01 8:57 ` [Xen-devel] " Jan Beulich
[not found] ` <5BB1E18802000078001ED127@suse.com>
2018-10-01 9:03 ` Juergen Gross
2018-10-01 9:18 ` Jan Beulich
2018-10-01 9:18 ` Jan Beulich
2018-10-10 11:53 ` David Woodhouse
2018-10-10 12:30 ` Thomas Gleixner
2018-10-10 12:30 ` Thomas Gleixner
2018-10-10 12:44 ` David Woodhouse
2018-10-10 12:47 ` Thomas Gleixner
2018-10-10 12:47 ` Thomas Gleixner
2018-10-10 13:38 ` Juergen Gross
2018-10-10 13:53 ` David Woodhouse
2018-10-10 13:53 ` David Woodhouse
2018-10-10 13:38 ` Juergen Gross
2018-10-10 12:44 ` David Woodhouse
2018-10-10 11:53 ` David Woodhouse
2018-10-01 7:37 ` [PATCH 0/2] xen: fix two issues in Xen pv qspinlock handling Juergen Gross
2018-10-01 7:37 ` Juergen Gross
2018-10-09 14:40 ` David Woodhouse
2018-10-09 14:52 ` Juergen Gross
2018-10-09 14:52 ` Juergen Gross
2018-10-09 14:40 ` David Woodhouse
2018-10-01 8:58 [Xen-devel] [PATCH 1/2] xen: fix race in xen_qlock_wait() Juergen Gross
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