Re: [PATCH] virtio_pci_modern: Use GFP_ATOMIC with spin_lock_irqsave held in virtqueue_exec_admin_cmd()

[David Laight <david.laight.linux@gmail.com>]

On Mon, 13 Apr 2026 03:45:20 -0400
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Mon, Apr 13, 2026 at 03:22:49PM +0800, Jinhui Guo wrote:
> > virtqueue_exec_admin_cmd() holds admin_vq->lock with spin_lock_irqsave(),
> > which disables interrupts.  Using GFP_KERNEL inside this critical section
> > is unsafe because kmalloc() may sleep, leading to potential deadlocks or
> > scheduling violations.
> > 
> > Switch to GFP_ATOMIC to ensure the allocation is non-blocking.
> > 
> > Fixes: 4c3b54af907e ("virtio_pci_modern: use completion instead of busy loop to wait on admin cmd result")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Jinhui Guo <guojinhui.liam@bytedance.com>
> > ---
> >  drivers/virtio/virtio_pci_modern.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> > index 6d8ae2a6a8ca..db8e4f88b749 100644
> > --- a/drivers/virtio/virtio_pci_modern.c
> > +++ b/drivers/virtio/virtio_pci_modern.c
> > @@ -101,7 +101,7 @@ static int virtqueue_exec_admin_cmd(struct virtio_pci_admin_vq *admin_vq,
> >  		return -EIO;
> >  
> >  	spin_lock_irqsave(&admin_vq->lock, flags);
> > -	ret = virtqueue_add_sgs(vq, sgs, out_num, in_num, cmd, GFP_KERNEL);
> > +	ret = virtqueue_add_sgs(vq, sgs, out_num, in_num, cmd, GFP_ATOMIC);
> >  	if (ret < 0) {
> >  		if (ret == -ENOSPC) {
> >  			spin_unlock_irqrestore(&admin_vq->lock, flags);  
> 
> 
> GFP_ATOMIC allocations can and will fail. If using them, one must
> retry, not just propagate failures.
> Or just switch admin_vq->lock to a mutex?

Or do the allocate before acquiring the lock (and free it not used
in the error path).

	David

> 
> 
> > -- 
> > 2.20.1  
> 
>