From: Jiang Liu <jiang.liu@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Bjorn Helgaas <bhelgaas@google.com>,
Randy Dunlap <rdunlap@infradead.org>,
Yinghai Lu <yinghai@kernel.org>, Borislav Petkov <bp@alien8.de>,
Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
x86@kernel.org, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Tony Luck <tony.luck@intel.com>, Joerg Roedel <joro@8bytes.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
linux-acpi@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [Patch v7 14/18] x86, irq, ACPI: Introduce a rwsem to protect IOAPIC operations from hotplug
Date: Sun, 02 Nov 2014 13:24:04 +0800 [thread overview]
Message-ID: <5455BFF4.6040401@linux.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1411011949370.5308@nanos>
On 2014/11/2 2:59, Thomas Gleixner wrote:
> On Mon, 27 Oct 2014, Jiang Liu wrote:
>> We are going to support ACPI based IOAPIC hotplug, so introduce a rwsem
>> to protect IOAPIC data structures from IOAPIC hotplug. We choose to
>> serialize in ACPI instead of in the IOAPIC core because:
>> 1) currently we are only plan to support ACPI based IOAPIC hotplug
>> 2) it's much more cleaner and easier
>> 3) It does't affect IOAPIC discovered by devicetree, SFI and mpparse.
>
> I had a last intensive look at this series as I was about to merge
> it. So I looked at the locking rules here again
>
>> +/*
>> + * Locks related to IOAPIC hotplug
>> + * Hotplug side:
>> + * ->lock_device_hotplug() //device_hotplug_lock
>> + * ->acpi_ioapic_rwsem
>> + * ->ioapic_lock
>> + * Interrupt mapping side:
>> + * ->acpi_ioapic_rwsem
>> + * ->ioapic_mutex
>> + * ->ioapic_lock
>> + */
>
> This looks sane, but I cannot figure out at all why this needs to be a
> rwsem.
>
>> +static DECLARE_RWSEM(acpi_ioapic_rwsem);
>
> I think it should be a simple mutex because the rwsem does not protect
> against concurrent execution what taken for read.
>
> And the site which takes it for write is in the early boot process
> where nothing runs in parallel AFAICT.
Hi Thomas,
You are right. It's not on hot path, so a mutex is better than
a rwsem here. I will send out an updated version soon.
Regards!
Gerry
>
> Thanks,
>
> tglx
>
next prev parent reply other threads:[~2014-11-02 5:24 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-27 5:21 [Patch v7 00/18] Enable support of IOAPIC hotplug on x86 platforms Jiang Liu
2014-10-27 5:21 ` [Patch v7 01/18] ACPI, irq: fix regression casued by 6b9fb7082409 Jiang Liu
2014-10-28 17:44 ` Pavel Machek
2014-10-28 18:13 ` Bjorn Helgaas
2014-10-28 18:45 ` Thomas Gleixner
2014-10-27 5:21 ` [Patch v7 02/18] x86, intel-mid: Create IRQs for APB timers and RTC timers Jiang Liu
2014-10-27 5:21 ` [Patch v7 03/18] ACPI, irq, x86: Return IRQ instead of GSI in mp_register_gsi() Jiang Liu
2014-10-27 5:21 ` [Patch v7 04/18] x86, PCI, ACPI: Kill private function resource_to_addr() in arch/x86/pci/acpi.c Jiang Liu
2014-10-27 5:21 ` [Patch v7 05/18] ACPI: Correct return value of acpi_dev_resource_address_space() Jiang Liu
2014-10-27 22:30 ` Rafael J. Wysocki
2014-10-27 22:49 ` Bjorn Helgaas
2014-10-27 23:11 ` Rafael J. Wysocki
2014-10-28 1:13 ` Bjorn Helgaas
2014-10-27 5:21 ` [Patch v7 06/18] ACPI: Fix minor syntax issues in processor_core.c Jiang Liu
2014-10-27 5:21 ` [Patch v7 07/18] ACPI: Add interfaces to parse IOAPIC ID for IOAPIC hotplug Jiang Liu
2014-10-27 5:21 ` [Patch v7 08/18] PCI: Remove PCI ioapic driver Jiang Liu
2014-10-27 5:21 ` [Patch v7 09/18] x86, irq: Split out alloc_ioapic_save_registers() Jiang Liu
2014-10-27 5:21 ` [Patch v7 10/18] x86, irq: Prefer assigned ID in APIC ID register for x86_64 Jiang Liu
2014-10-27 5:21 ` [Patch v7 11/18] x86, irq: Remove __init marker for functions will be used by IOAPIC hotplug Jiang Liu
2014-10-27 5:21 ` [Patch v7 12/18] x86, irq: Keep balance of IOAPIC pin reference count Jiang Liu
2014-10-27 5:21 ` [Patch v7 13/18] x86, irq: Refine mp_register_ioapic() to prepare for IOAPIC hotplug Jiang Liu
2014-10-27 5:21 ` [Patch v7 14/18] x86, irq, ACPI: Introduce a rwsem to protect IOAPIC operations from hotplug Jiang Liu
2014-11-01 18:59 ` Thomas Gleixner
2014-11-02 5:24 ` Jiang Liu [this message]
2014-10-27 5:21 ` [Patch v7 15/18] x86, irq, ACPI: Implement interface to support ACPI based IOAPIC hot-addition Jiang Liu
2014-10-27 5:21 ` [Patch v7 16/18] x86, irq, ACPI: Implement interfaces to support ACPI based IOAPIC hot-removal Jiang Liu
2014-10-27 5:21 ` [Patch v7 17/18] x86, irq: Introduce helper to check whether an IOAPIC has been registered Jiang Liu
2014-10-28 17:47 ` Pavel Machek
2014-10-27 5:21 ` [Patch v7 18/18] x86, irq, ACPI: Implement ACPI driver to support IOAPIC hotplug Jiang Liu
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