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[82.53.135.154]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499b3c556a3sm17318315e9.3.2026.08.20.01.59.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Aug 2026 01:59:18 -0700 (PDT) Date: Thu, 20 Aug 2026 10:59:13 +0200 From: Stefano Garzarella To: Andrey Drobyshev Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux.dev, netdev@vger.kernel.org, mst@redhat.com, stefanha@redhat.com, jasowangio@gmail.com, eperezma@redhat.com Subject: Re: [PATCH v2] vhost: clear vq->worker under vq->mutex when freeing workers Message-ID: References: <20260819114328.426131-1-andrey.drobyshev@virtuozzo.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260819114328.426131-1-andrey.drobyshev@virtuozzo.com> On Wed, Aug 19, 2026 at 02:43:28PM +0300, Andrey Drobyshev wrote: >Every other update of vq->worker is done under vq->mutex - the worker >attach/swap ioctls and vhost_worker_killed(). vhost_workers_free() is >the sole exception: it clears vq->worker without holding the lock. > >The effect is harmless in practice, as this only happens while the >owning process (and thus the whole device) is dying, but the lockless >write is inconsistent with the rest of the code. Clear vq->worker under >vq->mutex, like everyone else, so that all writers of vq->worker follow >the same locking rule. > >vhost_vq_reset() also used to clear vq->worker locklessly, earlier on >the same teardown path, making the write in vhost_workers_free() >redundant. Drop the clear from vhost_vq_reset() and initialize the >pointer in vhost_dev_init() instead, so that vhost_workers_free() is the >only place clearing vq->worker on teardown. Any work queued while >vq->worker is still set is drained by the synchronize_rcu() + >vhost_dev_flush() in vhost_workers_free() before the workers are freed. > >Reported-by: Sashiko Bot >Closes: https://lore.kernel.org/kvm/20260721102325.1BD6C1F00A3A@smtp.kernel.org >Link: https://lore.kernel.org/kvm/20260724153334.1BCBF1F000E9@smtp.kernel.org >Signed-off-by: Andrey Drobyshev >--- > >v1 -> v2: > > * Drop the lockless vq->worker clear from vhost_vq_reset(), initialize > vq->worker in vhost_dev_init() instead; > * Rebase onto Michael's mst/linux-next tree (with my previously merged > vsock patches); > * Add links to Sashiko reports and adjust commit message. > >v1: https://lore.kernel.org/kvm/20260723153310.745855-1-andrey.drobyshev@virtuozzo.com > > drivers/vhost/vhost.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > >diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c >index a0c1d54019aa..5764a54ddc92 100644 >--- a/drivers/vhost/vhost.c >+++ b/drivers/vhost/vhost.c >@@ -392,7 +392,6 @@ static void vhost_vq_reset(struct vhost_dev *dev, > vq->busyloop_timeout = 0; > vq->umem = NULL; > vq->iotlb = NULL; >- rcu_assign_pointer(vq->worker, NULL); > vhost_vring_call_reset(&vq->call_ctx); > __vhost_vq_meta_reset(vq); > } >@@ -613,6 +612,7 @@ void vhost_dev_init(struct vhost_dev *dev, > vq->heads = NULL; > vq->nheads = NULL; > vq->dev = dev; >+ RCU_INIT_POINTER(vq->worker, NULL); > mutex_init(&vq->mutex); > vhost_vq_reset(dev, vq); > if (vq->handle_kick) >@@ -722,13 +722,19 @@ static void vhost_worker_destroy(struct vhost_dev *dev, > static void vhost_workers_free(struct vhost_dev *dev) > { > struct vhost_worker *worker; >+ struct vhost_virtqueue *vq; nit: `vq` is used only in the for loop, so you can move this declaration inside the loop. (I'm not asking to respin for just this) > unsigned long i; > > if (!dev->use_worker) > return;) > >- for (i = 0; i < dev->nvqs; i++) >- rcu_assign_pointer(dev->vqs[i]->worker, NULL); >+ for (i = 0; i < dev->nvqs; i++) { >+ vq = dev->vqs[i]; >+ >+ mutex_lock(&vq->mutex); >+ rcu_assign_pointer(vq->worker, NULL); >+ mutex_unlock(&vq->mutex); >+ } > LGTM! Reviewed-by: Stefano Garzarella