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Thu, 05 Nov 2026 11:43:50 -0800 (PST) X-Received: by 2002:a05:600c:19cf:b0:4a1:fbf8:55c9 with SMTP id 5b1f17b1804b1-4b6dff85599mr2216835e9.33.1793907830232; Thu, 05 Nov 2026 11:43:50 -0800 (PST) Received: from redhat.com ([2a0d:6fc0:1401:db00:7367:7b9e:e66f:2b7d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b4527fed5bsm206845465e9.3.2026.11.05.11.43.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 11:43:49 -0800 (PST) Date: Thu, 5 Nov 2026 14:43:46 -0500 From: "Michael S. Tsirkin" To: Stjepan Poljak Cc: Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , Richard Weinberger , Anton Ivanov , Johannes Berg , Cornelia Huck , Halil Pasic , Eric Farman , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Alexander Graf , virtualization@lists.linux.dev, linux-um@lists.infradead.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] virtio_ring: return an error pointer from vring_create_virtqueue() Message-ID: <20261105144316-mutt-send-email-mst@kernel.org> References: <20261105193426.2999631-1-stjepan.poljak@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261105193426.2999631-1-stjepan.poljak@gmail.com> On Thu, Nov 05, 2026 at 08:34:25PM +0100, Stjepan Poljak wrote: > vring_create_virtqueue() and vring_create_virtqueue_map() return NULL > on any failure, so the error returned from vring_alloc_queue_split() > is lost and turned into -ENOMEM. This is especially misleading if > vring_alloc_queue_split() rejects a queue size with -EINVAL (i.e. if > queue size is not a power of two): > > virtio_blk virtio0: Bad virtqueue length 100 > virtio_blk virtio0: probe with driver virtio_blk failed with error -12 > > So the error points whoever debugs it at an allocation failure that > never happened. > > Return an ERR_PTR() instead: the error from vring_alloc_queue_split() > or vring_alloc_queue_packed(), or -ENOMEM when allocating the > virtqueue itself fails. Make the callers, virtio_pci (modern and > legacy), virtio_mmio, virtio_vdpa, virtio_ccw and virtio_uml, check > with IS_ERR() and pass the error on. The error path in virtio_ccw > deletes a non-NULL vq, so clear vq there before taking it. > > Co-Authored-By: Claude Opus 5.5 not how you ae supposed to attribute LLM use. > Signed-off-by: Stjepan Poljak > --- > Tested on x86_64 with a virtio-mmio virtio-blk device offering a > 100-entry queue: the probe now fails with -22 instead of -12, and a > 128-entry queue probes as before. The other transports are only > compile-tested (x86_64, ARCH=um, s390 with clang, W=1). > > No Fixes: tag, since the error has been -ENOMEM since 2010 and nothing > regressed. > > This conflicts trivially with patch 07/12 of Alexander Graf's "virtio: > support devices that own their virtqueue memory" v2: > https://lore.kernel.org/virtualization/20260818211425.91009-1-graf@amazon.com/ > --- > arch/um/drivers/virtio_uml.c | 4 ++-- > drivers/s390/virtio/virtio_ccw.c | 5 +++-- > drivers/virtio/virtio_mmio.c | 4 ++-- > drivers/virtio/virtio_pci_legacy.c | 4 ++-- > drivers/virtio/virtio_pci_modern.c | 4 ++-- > drivers/virtio/virtio_ring.c | 12 +++++++----- > drivers/virtio/virtio_vdpa.c | 4 ++-- > include/linux/virtio_ring.h | 6 +++++- > 8 files changed, 25 insertions(+), 18 deletions(-) > > diff --git a/arch/um/drivers/virtio_uml.c b/arch/um/drivers/virtio_uml.c > index 881c34098a74..8b645523277f 100644 > --- a/arch/um/drivers/virtio_uml.c > +++ b/arch/um/drivers/virtio_uml.c > @@ -984,8 +984,8 @@ static struct virtqueue *vu_setup_vq(struct virtio_device *vdev, > > vq = vring_create_virtqueue(index, num, PAGE_SIZE, vdev, true, true, > ctx, vu_notify, callback, info->name); > - if (!vq) { > - rc = -ENOMEM; > + if (IS_ERR(vq)) { > + rc = PTR_ERR(vq); > goto error_create; > } > vq->priv = info; > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c > index 552d77998012..c5a30f0a2bc2 100644 > --- a/drivers/s390/virtio/virtio_ccw.c > +++ b/drivers/s390/virtio/virtio_ccw.c > @@ -590,10 +590,11 @@ static struct virtqueue *virtio_ccw_setup_vq(struct virtio_device *vdev, > vdev, true, may_reduce, ctx, > notify, callback, name); > > - if (!vq) { > + if (IS_ERR(vq)) { > /* For now, we fail if we can't get the requested size. */ > dev_warn(&vcdev->cdev->dev, "no vq\n"); > - err = -ENOMEM; > + err = PTR_ERR(vq); > + vq = NULL; > goto out_err; > } > > diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c > index e2ec0ec01d67..c403a025006e 100644 > --- a/drivers/virtio/virtio_mmio.c > +++ b/drivers/virtio/virtio_mmio.c > @@ -396,8 +396,8 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned int in > /* Create the vring */ > vq = vring_create_virtqueue(index, num, VIRTIO_MMIO_VRING_ALIGN, vdev, > true, true, ctx, notify, callback, name); > - if (!vq) { > - err = -ENOMEM; > + if (IS_ERR(vq)) { > + err = PTR_ERR(vq); > goto error_new_virtqueue; > } > > diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c > index 8115aa39e01e..9d94fffff344 100644 > --- a/drivers/virtio/virtio_pci_legacy.c > +++ b/drivers/virtio/virtio_pci_legacy.c > @@ -130,8 +130,8 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev, > VIRTIO_PCI_VRING_ALIGN, &vp_dev->vdev, > true, false, ctx, > vp_notify, callback, name); > - if (!vq) > - return ERR_PTR(-ENOMEM); > + if (IS_ERR(vq)) > + return vq; > > vq->num_max = num; > > diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c > index 922e2df027de..28ccb2130e27 100644 > --- a/drivers/virtio/virtio_pci_modern.c > +++ b/drivers/virtio/virtio_pci_modern.c > @@ -720,8 +720,8 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev, > SMP_CACHE_BYTES, &vp_dev->vdev, > true, true, ctx, > notify, callback, name); > - if (!vq) > - return ERR_PTR(-ENOMEM); > + if (IS_ERR(vq)) > + return vq; > > vq->num_max = num; > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index f683a2d6a200..6dd4a7651bde 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -1421,13 +1421,13 @@ static struct virtqueue *vring_create_virtqueue_split( > err = vring_alloc_queue_split(&vring_split, vdev, num, vring_align, > may_reduce_num, map); > if (err) > - return NULL; > + return ERR_PTR(err); > > vq = __vring_new_virtqueue_split(index, &vring_split, vdev, weak_barriers, > context, notify, callback, name, map); > if (!vq) { > vring_free_split(&vring_split, vdev, map); > - return NULL; > + return ERR_PTR(-ENOMEM); > } > > to_vvq(vq)->we_own_ring = true; > @@ -2671,15 +2671,17 @@ static struct virtqueue *vring_create_virtqueue_packed( > { > struct vring_virtqueue_packed vring_packed = {}; > struct virtqueue *vq; > + int err; > > - if (vring_alloc_queue_packed(&vring_packed, vdev, num, map)) > - return NULL; > + err = vring_alloc_queue_packed(&vring_packed, vdev, num, map); > + if (err) > + return ERR_PTR(err); > > vq = __vring_new_virtqueue_packed(index, &vring_packed, vdev, weak_barriers, > context, notify, callback, name, map); > if (!vq) { > vring_free_packed(&vring_packed, vdev, map); > - return NULL; > + return ERR_PTR(-ENOMEM); > } > > to_vvq(vq)->we_own_ring = true; > diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c > index f9559b6b2e0b..c1b6134b2267 100644 > --- a/drivers/virtio/virtio_vdpa.c > +++ b/drivers/virtio/virtio_vdpa.c > @@ -208,8 +208,8 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index, > vq = vring_create_virtqueue_map(index, max_num, align, vdev, > true, may_reduce_num, ctx, > notify, callback, name, map); > - if (!vq) { > - err = -ENOMEM; > + if (IS_ERR(vq)) { > + err = PTR_ERR(vq); > goto error_new_virtqueue; > } > > diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h > index c97a12c1cda3..c808ca7e8d58 100644 > --- a/include/linux/virtio_ring.h > +++ b/include/linux/virtio_ring.h > @@ -66,6 +66,9 @@ struct device; > * may_reduce_num is set, then this may allocate a smaller ring than > * expected. The caller should query virtqueue_get_vring_size to learn > * the actual size of the ring. > + * > + * Returns the virtqueue or an ERR_PTR() on failure: -EINVAL if num is > + * not a valid ring size, -ENOMEM if the ring could not be allocated. > */ > struct virtqueue *vring_create_virtqueue(unsigned int index, > unsigned int num, > @@ -80,7 +83,8 @@ struct virtqueue *vring_create_virtqueue(unsigned int index, > > /* > * Creates a virtqueue and allocates the descriptor ring with per > - * virtqueue mapping operations. > + * virtqueue mapping operations. Returns the virtqueue or an ERR_PTR() > + * on failure, like vring_create_virtqueue(). > */ > struct virtqueue *vring_create_virtqueue_map(unsigned int index, > unsigned int num, > > base-commit: 1a577f9402c1780cc1e663f48d5dd54c02051b09 > -- > 2.53.0