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nvdimm: virtio_pmem: serialize flush requests

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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: 6e84200c0a ("virtio-pmem: Add virtio pmem driver")
Signed-off-by: Li Chen <me@linux.beauty>
Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://patch.msgid.link/20260203021353.121091-1-me@linux.beauty
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
This commit is contained in:
Li Chen 2026-02-03 10:13:51 +08:00 • committed by Ira Weiny
parent 9c0fc1d37f
commit a9ba6733c7
3 changed files with 7 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

3
drivers/nvdimm/nd_virtio.c
View file

@ -44,6 +44,8 @@ static int virtio_pmem_flush(struct nd_region *nd_region)
unsigned long flags;
int err, err1;
guard(mutex)(&vpmem->flush_lock);
/*
* Don't bother to submit the request to the device if the device is
* not activated.
@ -53,7 +55,6 @@ static int virtio_pmem_flush(struct nd_region *nd_region)
return -EIO;
}
might_sleep();
req_data = kmalloc(sizeof(*req_data), GFP_KERNEL);
if (!req_data)
return -ENOMEM;

1
drivers/nvdimm/virtio_pmem.c
View file

@ -64,6 +64,7 @@ static int virtio_pmem_probe(struct virtio_device *vdev)
goto out_err;
}
mutex_init(&vpmem->flush_lock);
vpmem->vdev = vdev;
vdev->priv = vpmem;
err = init_vq(vpmem);

4
drivers/nvdimm/virtio_pmem.h
View file

@ -13,6 +13,7 @@
#include <linux/module.h>
#include <uapi/linux/virtio_pmem.h>
#include <linux/libnvdimm.h>
#include <linux/mutex.h>
#include <linux/spinlock.h>
struct virtio_pmem_request {
@ -35,6 +36,9 @@ struct virtio_pmem {
/* Virtio pmem request queue */
struct virtqueue *req_vq;
/* Serialize flush requests to the device. */
struct mutex flush_lock;
/* nvdimm bus registers virtio pmem device */
struct nvdimm_bus *nvdimm_bus;
struct nvdimm_bus_descriptor nd_desc;