linux-kernel - Re: [PATCH V3 3/3] vdpa_sim: flush workers on suspend

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Message-ID: <46f91e76-6f88-4f83-8854-10baed4e82c9@oracle.com>
Date: Tue, 21 May 2024 09:39:12 -0400
From: Steven Sistare <steven.sistare@...cle.com>
To: Jason Wang <jasowang@...hat.com>
Cc: virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Si-Wei Liu <si-wei.liu@...cle.com>,
        Eugenio Perez Martin <eperezma@...hat.com>,
        Xie Yongji <xieyongji@...edance.com>,
        Stefano Garzarella <sgarzare@...hat.com>
Subject: Re: [PATCH V3 3/3] vdpa_sim: flush workers on suspend

On 5/20/2024 10:32 PM, Jason Wang wrote:
> On Mon, May 20, 2024 at 11:21 PM Steve Sistare
> <steven.sistare@...cle.com> wrote:
>>
>> Flush to guarantee no workers are running when suspend returns.
>> Add a lock to enforce ordering between clearing running, flushing,
>> and posting new work in vdpasim_kick_vq.  It must be a spin lock
>> because vdpasim_kick_vq may be reached va eventfd_write.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@...cle.com>
>> ---
>>   drivers/vdpa/vdpa_sim/vdpa_sim.c | 16 ++++++++++++++--
>>   drivers/vdpa/vdpa_sim/vdpa_sim.h |  1 +
>>   2 files changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> index 8ffea8430f95..67ed49d95bf0 100644
>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>> @@ -322,7 +322,7 @@ static u16 vdpasim_get_vq_size(struct vdpa_device *vdpa, u16 idx)
>>                  return VDPASIM_QUEUE_MAX;
>>   }
>>
>> -static void vdpasim_kick_vq(struct vdpa_device *vdpa, u16 idx)
>> +static void vdpasim_do_kick_vq(struct vdpa_device *vdpa, u16 idx)
>>   {
>>          struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>>          struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
>> @@ -337,6 +337,15 @@ static void vdpasim_kick_vq(struct vdpa_device *vdpa, u16 idx)
>>                  vdpasim_schedule_work(vdpasim);
>>   }
>>
>> +static void vdpasim_kick_vq(struct vdpa_device *vdpa, u16 idx)
>> +{
>> +       struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>> +
>> +       spin_lock(&vdpasim->kick_lock);
>> +       vdpasim_do_kick_vq(vdpa, idx);
>> +       spin_unlock(&vdpasim->kick_lock);
>> +}
>> +
>>   static void vdpasim_set_vq_cb(struct vdpa_device *vdpa, u16 idx,
>>                                struct vdpa_callback *cb)
>>   {
>> @@ -520,8 +529,11 @@ static int vdpasim_suspend(struct vdpa_device *vdpa)
>>          struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>>
>>          mutex_lock(&vdpasim->mutex);
>> +       spin_lock(&vdpasim->kick_lock);
>>          vdpasim->running = false;
>> +       spin_unlock(&vdpasim->kick_lock);
>>          mutex_unlock(&vdpasim->mutex);
>> +       kthread_flush_work(&vdpasim->work);
>>
>>          return 0;
>>   }
>> @@ -537,7 +549,7 @@ static int vdpasim_resume(struct vdpa_device *vdpa)
>>          if (vdpasim->pending_kick) {
>>                  /* Process pending descriptors */
>>                  for (i = 0; i < vdpasim->dev_attr.nvqs; ++i)
>> -                       vdpasim_kick_vq(vdpa, i);
>> +                       vdpasim_do_kick_vq(vdpa, i);
>>
>>                  vdpasim->pending_kick = false;
>>          }
>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
>> index bb137e479763..5eb6ca9c5ec5 100644
>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
>> @@ -75,6 +75,7 @@ struct vdpasim {
>>          bool pending_kick;
>>          /* spinlock to synchronize iommu table */
>>          spinlock_t iommu_lock;
>> +       spinlock_t kick_lock;
> 
> It looks to me this is not initialized?

Yup, I lost that line while fiddling with different locking schemes.
Thanks, will fix in V4.

@@ -236,6 +236,7 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr 
*dev_attr,

         mutex_init(&vdpasim->mutex);
         spin_lock_init(&vdpasim->iommu_lock);
+       spin_lock_init(&vdpasim->kick_lock);

With that fix, does this patch earn your RB?

- Steve

>>   };
>>
>>   struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *attr,
>> --
>> 2.39.3
>>
>