From a9ba6733c7f1096c4506bf4e34a546e07242df74 Mon Sep 17 00:00:00 2001 From: Li Chen Date: Tue, 3 Feb 2026 10:13:51 +0800 Subject: [PATCH] nvdimm: virtio_pmem: serialize flush requests 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 Acked-by: Pankaj Gupta Acked-by: Michael S. Tsirkin Link: https://patch.msgid.link/20260203021353.121091-1-me@linux.beauty Signed-off-by: Ira Weiny --- drivers/nvdimm/nd_virtio.c | 3 ++- drivers/nvdimm/virtio_pmem.c | 1 + drivers/nvdimm/virtio_pmem.h | 4 ++++ 3 files changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c index c3f07be4aa22..af82385be7c6 100644 --- a/drivers/nvdimm/nd_virtio.c +++ b/drivers/nvdimm/nd_virtio.c @@ -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; diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c index 2396d19ce549..77b196661905 100644 --- a/drivers/nvdimm/virtio_pmem.c +++ b/drivers/nvdimm/virtio_pmem.c @@ -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); diff --git a/drivers/nvdimm/virtio_pmem.h b/drivers/nvdimm/virtio_pmem.h index 0dddefe594c4..f72cf17f9518 100644 --- a/drivers/nvdimm/virtio_pmem.h +++ b/drivers/nvdimm/virtio_pmem.h @@ -13,6 +13,7 @@ #include #include #include +#include #include 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; -- 2.47.3