Re: [Qemu-devel] [patch v4 12/16] e1000: apply fine lock on e1000

[Jan Kiszka <jan.kiszka@web.de>]

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On 2012-10-24 08:31, liu ping fan wrote:
> On Tue, Oct 23, 2012 at 5:04 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>> On 2012-10-22 11:23, Liu Ping Fan wrote:
>>> Use local lock to protect e1000. When calling the system function,
>>> dropping the fine lock before acquiring the big lock. This will
>>> introduce broken device state, which need extra effort to fix.
>>>
>>> Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
>>> ---
>>>  hw/e1000.c |   24 +++++++++++++++++++++++-
>>>  1 files changed, 23 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/hw/e1000.c b/hw/e1000.c
>>> index ae8a6c5..5eddab5 100644
>>> --- a/hw/e1000.c
>>> +++ b/hw/e1000.c
>>> @@ -85,6 +85,7 @@ typedef struct E1000State_st {
>>>      NICConf conf;
>>>      MemoryRegion mmio;
>>>      MemoryRegion io;
>>> +    QemuMutex e1000_lock;
>>>
>>>      uint32_t mac_reg[0x8000];
>>>      uint16_t phy_reg[0x20];
>>> @@ -223,13 +224,27 @@ static const uint32_t mac_reg_init[] = {
>>>  static void
>>>  set_interrupt_cause(E1000State *s, int index, uint32_t val)
>>>  {
>>> +    QemuThread *t;
>>> +
>>>      if (val && (E1000_DEVID >= E1000_DEV_ID_82547EI_MOBILE)) {
>>>          /* Only for 8257x */
>>>          val |= E1000_ICR_INT_ASSERTED;
>>>      }
>>>      s->mac_reg[ICR] = val;
>>>      s->mac_reg[ICS] = val;
>>> -    qemu_set_irq(s->dev.irq[0], (s->mac_reg[IMS] & s->mac_reg[ICR]) != 0);
>>> +
>>> +    t = pthread_getspecific(qemu_thread_key);
>>> +    if (t->context_type == 1) {
>>> +        qemu_mutex_unlock(&s->e1000_lock);
>>> +        qemu_mutex_lock_iothread();
>>> +    }
>>> +    if (DEVICE(s)->state < DEV_STATE_STOPPING) {
>>> +        qemu_set_irq(s->dev.irq[0], (s->mac_reg[IMS] & s->mac_reg[ICR]) != 0);
>>> +    }
>>> +    if (t->context_type == 1) {
>>> +        qemu_mutex_unlock_iothread();
>>> +        qemu_mutex_lock(&s->e1000_lock);
>>> +    }
>>
>> This is ugly for many reasons. First of all, it is racy as the register
>> content may change while dropping the device lock, no? Then you would
>> raise or clear an IRQ spuriously.
>>
> Device state's intact is protected by busy flag, and will not broken

Except that the busy flag concept is broken in itself.

I see that we have a all-or-nothing problem here: to address this
properly, we need to convert the IRQ path to lock-less (or at least
compatible with holding per-device locks) as well.

Jan


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