From: "Jan Beulich" <JBeulich@suse.com>
To: Feng Wu <feng.wu@intel.com>
Cc: george.dunlap@eu.citrix.com, andrew.cooper3@citrix.com,
dario.faggioli@citrix.com, kevin.tian@intel.com,
xen-devel@lists.xen.org
Subject: Re: [PATCH v4 6/6] VMX: Fixup PI descritpor when cpu is offline
Date: Mon, 26 Sep 2016 07:03:22 -0600 [thread overview]
Message-ID: <57E938BA020000780011275C@prv-mh.provo.novell.com> (raw)
In-Reply-To: <1474425470-3629-7-git-send-email-feng.wu@intel.com>
>>> On 21.09.16 at 04:37, <feng.wu@intel.com> wrote:
> +void vmx_pi_desc_fixup(int cpu)
> +{
> + unsigned int new_cpu, dest;
> + unsigned long flags;
> + struct arch_vmx_struct *vmx, *tmp;
> + spinlock_t *new_lock, *old_lock = &per_cpu(vmx_pi_blocking, cpu).lock;
> + struct list_head *blocked_vcpus = &per_cpu(vmx_pi_blocking, cpu).list;
> +
> + if ( !iommu_intpost )
> + return;
> +
> + spin_lock_irqsave(old_lock, flags);
> +
> + list_for_each_entry_safe(vmx, tmp, blocked_vcpus, pi_blocking.list)
> + {
> + /*
> + * We need to find an online cpu as the NDST of the PI descriptor, it
> + * doesn't matter whether it is within the cpupool of the domain or
> + * not. As long as it is online, the vCPU will be woken up once the
> + * notification event arrives.
> + */
> + new_cpu = cpumask_any(&cpu_online_map);
> + new_lock = &per_cpu(vmx_pi_blocking, new_cpu).lock;
> +
> + spin_lock(new_lock);
Without extra consideration this is a classical ABBA deadlock
scenario. Please add a comment (perhaps at the first lock location
above) at least briefly explaining why there can't be any deadlock
here.
Apart from that the patch looks fine to me now.
Jan
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next prev parent reply other threads:[~2016-09-26 13:03 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-21 2:37 [PATCH v4 0/6] VMX: Properly handle pi descriptor and per-cpu blocking list Feng Wu
2016-09-21 2:37 ` [PATCH v4 1/6] VMX: Statically assign two PI hooks Feng Wu
2016-09-26 11:37 ` Jan Beulich
2016-09-26 12:09 ` Jan Beulich
2016-09-28 6:48 ` Wu, Feng
2016-09-28 9:38 ` Jan Beulich
2016-10-09 8:30 ` Wu, Feng
2016-10-10 7:26 ` Jan Beulich
2016-09-21 2:37 ` [PATCH v4 2/6] VMX: Properly handle pi when all the assigned devices are removed Feng Wu
2016-09-26 11:46 ` Jan Beulich
2016-09-28 6:50 ` Wu, Feng
2016-09-28 9:52 ` Jan Beulich
2016-09-29 3:08 ` Wu, Feng
2016-09-21 2:37 ` [PATCH v4 3/6] VMX: Cleanup PI per-cpu blocking list when vcpu is destroyed Feng Wu
2016-09-21 2:37 ` [PATCH v4 4/6] VMX: Make sure PI is in proper state before install the hooks Feng Wu
2016-09-26 12:45 ` Jan Beulich
2016-09-28 6:50 ` Wu, Feng
2016-09-21 2:37 ` [PATCH v4 5/6] VT-d: No need to set irq affinity for posted format IRTE Feng Wu
2016-09-26 12:58 ` Jan Beulich
2016-09-28 6:51 ` Wu, Feng
2016-09-28 9:58 ` Jan Beulich
2016-10-09 5:35 ` Wu, Feng
2016-10-10 7:02 ` Jan Beulich
2016-10-10 22:55 ` Wu, Feng
2016-09-21 2:37 ` [PATCH v4 6/6] VMX: Fixup PI descritpor when cpu is offline Feng Wu
2016-09-26 13:03 ` Jan Beulich [this message]
2016-09-28 6:53 ` Wu, Feng
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