Re: [PATCH v4 03/18] mshv: Fix race in mshv_irqfd_deassign

[Anirudh Rayabharam <anirudh@anirudhrb.com>]

On Thu, May 07, 2026 at 03:43:15PM +0000, Stanislav Kinsburskii wrote:
> mshv_irqfd_deactivate() and the hlist traversal of pt_irqfds_list
> require pt->pt_irqfds_lock to be held, but mshv_irqfd_deassign()
> omits it. This races with the EPOLLHUP path in mshv_irqfd_wakeup(),
> which does take the lock before calling mshv_irqfd_deactivate().
> 
> Additionally, mshv_irqfd_deactivate() uses hlist_del() which poisons
> the node pointers rather than resetting them. Since
> mshv_irqfd_is_active() relies on hlist_unhashed() (checks pprev ==
> NULL), a poisoned node still appears active. If a concurrent path calls
> mshv_irqfd_deactivate() again on the same irqfd, the guard fails to
> prevent a double hlist_del() on poisoned pointers.
> 
> Fix both issues:
> - Add the missing spin_lock_irq/spin_unlock_irq around the list
>   traversal in mshv_irqfd_deassign(), matching mshv_irqfd_release().
> - Use hlist_del_init() instead of hlist_del() so the node is properly
>   marked as unhashed after removal, making the is_active guard reliable.
> 
> Fixes: 621191d709b14 ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs")
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> ---
>  drivers/hv/mshv_eventfd.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>