Re: [PATCH v2] nvdimm: virtio_pmem: serialize flush requests

[Ira Weiny <ira.weiny@intel.com>]

Michael S. Tsirkin wrote:
> On Tue, Feb 03, 2026 at 10:13:51AM +0800, Li Chen wrote:
> > Under heavy concurrent flush traffic, virtio-pmem can overflow its request
> > virtqueue (req_vq): virtqueue_add_sgs() starts returning -ENOSPC and the
> > driver logs "no free slots in the virtqueue". Shortly after that the
> > device enters VIRTIO_CONFIG_S_NEEDS_RESET and flush requests fail with
> > "virtio pmem device needs a reset".
> > 
> > Serialize virtio_pmem_flush() with a per-device mutex so only one flush
> > request is in-flight at a time. This prevents req_vq descriptor overflow
> > under high concurrency.
> > 
> > Reproducer (guest with virtio-pmem):
> >   - mkfs.ext4 -F /dev/pmem0
> >   - mount -t ext4 -o dax,noatime /dev/pmem0 /mnt/bench
> >   - fio: ioengine=io_uring rw=randwrite bs=4k iodepth=64 numjobs=64
> >         direct=1 fsync=1 runtime=30s time_based=1
> >   - dmesg: "no free slots in the virtqueue"
> >            "virtio pmem device needs a reset"
> > 
> > Fixes: 6e84200c0a29 ("virtio-pmem: Add virtio pmem driver")
> > Signed-off-by: Li Chen <me@linux.beauty>
> 
> 
> Thanks!
> And the commit message looks good now and includes the
> reproducer.
> 
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> 
> Ira are you picking this up?
> 

Yes queued for 7.0

Ira

[snip]