From mboxrd@z Thu Jan 1 00:00:00 1970 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 B5217283FCF; Tue, 3 Feb 2026 02:14:26 +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=1770084868; cv=pass; b=UBEabvD3QLR04zWBYhU/blMMFnXHM1ms6hiC4tVgsz1G8A31+dmL8bDNnpHoRenXFEClcIsUUA0MbFIOIVu5mnS444HP4Xb793jKcetjUjF+mM/3jVFVJETUZAkbeHWfBnpQSTSZe1UQrA+Z1+tnxMGbLebbhIrtwpO+OcSosuU= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770084868; c=relaxed/simple; bh=WEWhjNjgMTivhK1+Z3T+JZM4cBxsWzERCWLL8mqoxzQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=gpPfDVMV8hf3iJwFIT64l7polQzu9vq9qNxLltEdvfgkG/rMMpOZygX6faVQTfTb4MAyAODfvhwIIkV160ojHRTuqCC3IMevwiwySMoB1a/CBXP2CxBWckje2ym0LFX3FG10mTttqfxq7jOYXSDpPmb2pRGc2MkErX/gFgQ+frY= 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=QaE3k+Wm; 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="QaE3k+Wm" ARC-Seal: i=1; a=rsa-sha256; t=1770084855; cv=none; d=zohomail.com; s=zohoarc; b=E/mHbg3eB+6FQr/BtveC7fDluD+mFkXEZsbud/PidyJSxTl/wouo6mrYNmFHSAHR5GcqkHBnE8lj1WFk8Xj5hzO6PLWNHp/sU0mUZDY6uIPb/EaM94HesZ7M9casC2U6CS9K1oBKi0mFy/MnxRdK+NEkkIsWXhidMogL87mXhK4= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1770084855; h=Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:MIME-Version:Message-ID:Subject:Subject:To:To:Message-Id:Reply-To; bh=EllBWXmAPg3ovIJDYXMDe9Fex2OSK19yvQg5WdHQF4w=; b=XUWkdi7oIVbt/udwU7tAfFVh/a6FxIwmZF43g/Fgi+JQaEDJevdfL7A+1nt8jx/bWeYUWfCbcUsIAxMhBHrB+CUEIIVYSLKap3ak/7S8rpu96oK+R/LD3o4v89VY8J70QsbN5ZYHORWuVGjr6OjXYV+TUi96viqLVbdvTYvKFLk= 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=1770084855; 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=EllBWXmAPg3ovIJDYXMDe9Fex2OSK19yvQg5WdHQF4w=; b=QaE3k+Wmh/gx5qr1Upm0qL0Inj7PEa6EA3QAMU+BD3uK7dQbecfcIgDfF8aFHImG 7MEJx0odQe04kz7LqQrluT0/3OFnP3bsNGzYqqD5w9ypzLKaeLAUfEWwU7EyzdbxdT+ exGHEs5o2//4MHs4zteLybWsY17lxJ4ALPsgnoKs= Received: by mx.zohomail.com with SMTPS id 1770084853055993.3306336899888; Mon, 2 Feb 2026 18:14:13 -0800 (PST) From: Li Chen To: Pankaj Gupta , Dan Williams , Vishal Verma , Dave Jiang , Ira Weiny , Cornelia Huck , "Michael S. Tsirkin" , Yuval Shaia , virtualization@lists.linux.dev, nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org Cc: Li Chen Subject: [PATCH v2] nvdimm: virtio_pmem: serialize flush requests Date: Tue, 3 Feb 2026 10:13:51 +0800 Message-ID: <20260203021353.121091-1-me@linux.beauty> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-ZohoMailClient: External 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 --- v2: - Use guard(mutex)() for flush_lock (as suggested by Ira Weiny). - Drop redundant might_sleep() next to guard(mutex)() (as suggested by Michael S. Tsirkin). 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; -- 2.52.0