From nobody Sun Feb 8 05:29:25 2026 Received: from sender4-pp-f112.zoho.com (sender4-pp-f112.zoho.com [136.143.188.112]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 415B72EBB90 for ; Tue, 13 Jan 2026 03:46:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=136.143.188.112 ARC-Seal: i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768275975; cv=pass; b=QiRvEDAq8nBXMz+dad7JhzssxEfivrEFBL6Ts1UgS/3yjFOle0RxG/+q2vGFirLpAbQvluYmGXlfCSiWhWq5uBa00xOvK3geAyHnHRHjUPGYLGiXIvFAv48sgJNT17xYP6bd96r0lAQthWEtknxBqOKJ438bRDqztdbl7lUSkfE= ARC-Message-Signature: i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768275975; c=relaxed/simple; bh=yh9WKYXlqUWc5sUsf/ucPYJFwqnKd9qWuYQzeplS0gA=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=NIf5Lm9yEZL1LKtL5N7GSghqd0JjMTJJsep4PHeqmiulIt38Vgu3fYWUEIMcWeAwXhaxX/tw97+LLDqOw4mO7Q39x2QlfiOVmnLpm6H2hbMUUcu2U3ubzCQLuDpG1TJIORm7ehrgsbT6G5AkFkJsMAYcSpl+ZI/C1MB9PVQdMzA= ARC-Authentication-Results: i=2; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=linux.beauty; spf=pass smtp.mailfrom=linux.beauty; dkim=pass (1024-bit key) header.d=linux.beauty header.i=me@linux.beauty header.b=hNfzTEga; arc=pass smtp.client-ip=136.143.188.112 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=linux.beauty Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.beauty Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.beauty header.i=me@linux.beauty header.b="hNfzTEga" ARC-Seal: i=1; a=rsa-sha256; t=1768275963; cv=none; d=zohomail.com; s=zohoarc; b=EZAxQBijCn6Z8Q9Ti677VQ/Pu4qOdsBzKWQ+sS4CwOyFWooPFsy1x4VoPxiWcAPnFp8g7CNHXV+ZA1lQkO/KjWt/n8fjqGnXOdWIl7tT9FWbaaLdA3ZzPRqdXnz9aJhdhtFK+hvJFW5uB9nhcxdGAtCaEa0G3DCTIZQ7eQYUjBU= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1768275963; h=Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:MIME-Version:Message-ID:Subject:Subject:To:To:Message-Id:Reply-To; bh=rLeMQF3euqQFHPcQ7Xuf1HGkbhRTdazc0FH9LsglTVo=; b=ZVl0g3qYzlz0TWDLDPVItHJaPeNO+iI7/Q4FommzLYpGIoBMbNw9/AhqtUEhJZAJiLIq0KVpDXkubTtwTIoC14LRRJd9xzPsjS3OO8XX9s022Nmunp4NpGBNYnlAfVuFiik9ehE0UEt9TT4+gxE5vw/9Ga7zOvwczOLO0VFhga0= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=linux.beauty; spf=pass smtp.mailfrom=me@linux.beauty; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1768275963; s=zmail; d=linux.beauty; i=me@linux.beauty; h=From:From:To:To:Cc:Cc:Subject:Subject:Date:Date:Message-ID:MIME-Version:Content-Transfer-Encoding:Message-Id:Reply-To; bh=rLeMQF3euqQFHPcQ7Xuf1HGkbhRTdazc0FH9LsglTVo=; b=hNfzTEgaNb7r7XF9rZgSUSdUHZ8pYeTShGa4T7wVDor+vouZtYtyBkWwVssmLjBI DxLZRRERi85UmFgOk44r2fwojTgP+2nVTb22VtnhBsaQJJbj/UvTMNz1vBuwSwn7dG9 +7YSXYqOVrKQ7B9YLS2BfChK5u5bRnOaSAd0a1DY= Received: by mx.zohomail.com with SMTPS id 1768275959721742.5854641970693; Mon, 12 Jan 2026 19:45:59 -0800 (PST) From: Li Chen To: Dan Williams , Vishal Verma , Dave Jiang , Ira Weiny , Pankaj Gupta , "Michael S. Tsirkin" , Cornelia Huck , Jakub Staron , nvdimm@lists.linux.dev, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Cc: Li Chen Subject: [PATCH] nvdimm: virtio_pmem: serialize flush requests Date: Tue, 13 Jan 2026 11:45:52 +0800 Message-ID: <20260113034552.62805-1-me@linux.beauty> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ZohoMailClient: External Content-Type: text/plain; charset="utf-8" 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=3Dio_uring rw=3Drandwrite bs=3D4k iodepth=3D64 numjobs=3D= 64 direct=3D1 fsync=3D1 runtime=3D30s time_based=3D1 - 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 --- drivers/nvdimm/nd_virtio.c | 15 +++++++++++---- drivers/nvdimm/virtio_pmem.c | 1 + drivers/nvdimm/virtio_pmem.h | 4 ++++ 3 files changed, 16 insertions(+), 4 deletions(-) diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c index c3f07be4aa22..827a17fe7c71 100644 --- a/drivers/nvdimm/nd_virtio.c +++ b/drivers/nvdimm/nd_virtio.c @@ -44,19 +44,24 @@ static int virtio_pmem_flush(struct nd_region *nd_regio= n) unsigned long flags; int err, err1; =20 + might_sleep(); + mutex_lock(&vpmem->flush_lock); + /* * Don't bother to submit the request to the device if the device is * not activated. */ if (vdev->config->get_status(vdev) & VIRTIO_CONFIG_S_NEEDS_RESET) { dev_info(&vdev->dev, "virtio pmem device needs a reset\n"); - return -EIO; + err =3D -EIO; + goto out_unlock; } =20 - might_sleep(); req_data =3D kmalloc(sizeof(*req_data), GFP_KERNEL); - if (!req_data) - return -ENOMEM; + if (!req_data) { + err =3D -ENOMEM; + goto out_unlock; + } =20 req_data->done =3D false; init_waitqueue_head(&req_data->host_acked); @@ -103,6 +108,8 @@ static int virtio_pmem_flush(struct nd_region *nd_regio= n) } =20 kfree(req_data); +out_unlock: + mutex_unlock(&vpmem->flush_lock); return err; }; =20 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; } =20 + mutex_init(&vpmem->flush_lock); vpmem->vdev =3D vdev; vdev->priv =3D vpmem; err =3D 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 =20 struct virtio_pmem_request { @@ -35,6 +36,9 @@ struct virtio_pmem { /* Virtio pmem request queue */ struct virtqueue *req_vq; =20 + /* 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; --=20 2.52.0