Re: [PATCH v2] xen-blkfront: unbind irq before tearing down ring and shadow requests

[Roger Pau Monné]

On Tue, Sep 22, 2026 at 03:21:55PM +0800, Yuchao Zhang wrote:
> In blkif_free_ring(), the driver tears down the ring's persistent grants,
> shadow request arrays, and shared ring structure (xenbus_teardown_ring),
> and only calls unbind_from_irqhandler() at the very end.
> 
> While blkif_free_ring() is freeing persistent grants and clearing the
> shadow array, the event channel interrupt (blkif_interrupt) is still
> registered and active.  If an interrupt arrives from the backend during
> this teardown window, blkif_interrupt() reads rinfo->ring.sring and,
> via blkif_completion(), accesses rinfo->shadow[id].grants_used and
> rinfo->shadow[id].sg.  blkif_free_ring() tears these structures down
> without holding rinfo->ring_lock, and the handler only checks
> info->connected at entry, so this is a real race resulting in a
> use-after-free or NULL pointer dereference.
> 
> Fix this by moving unbind_from_irqhandler() to the beginning of
> blkif_free_ring().  Calling unbind_from_irqhandler() first frees the
> IRQ and synchronizes with any in-flight interrupt handlers on other CPUs
> before ring memory and shadow request structures are deallocated,
> matching the teardown order in drivers/net/xen-netfront.c.
> 
> Fixes: 11659569f720 ("xen/blkfront: split per device io_lock")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Yuchao Zhang <ndaugoing@xxxxxxxxx>

Acked-by: Roger Pau Monné <roger@xxxxxxxxxxxxxx>

Thanks, Roger.