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mshv: Fix race in mshv_irqfd_deassign

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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: 621191d709 ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs")
Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
This commit is contained in:
Stanislav Kinsburskii 2026-05-07 15:43:15 +00:00 committed by Wei Liu
parent 5cb5c2f4a8
commit 0762262ac3
1 changed files with 3 additions and 2 deletions
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5
drivers/hv/mshv_eventfd.c
View File

@ -284,7 +284,7 @@ static void mshv_irqfd_deactivate(struct mshv_irqfd *irqfd)
if (!mshv_irqfd_is_active(irqfd))
return;
hlist_del(&irqfd->irqfd_hnode);
hlist_del_init(&irqfd->irqfd_hnode);
queue_work(irqfd_cleanup_wq, &irqfd->irqfd_shutdown);
}
@ -541,13 +541,14 @@ static int mshv_irqfd_deassign(struct mshv_partition *pt,
if (IS_ERR(eventfd))
return PTR_ERR(eventfd);
spin_lock_irq(&pt->pt_irqfds_lock);
hlist_for_each_entry_safe(irqfd, n, &pt->pt_irqfds_list,
irqfd_hnode) {
if (irqfd->irqfd_eventfd_ctx == eventfd &&
irqfd->irqfd_irqnum == args->gsi)
mshv_irqfd_deactivate(irqfd);
}
spin_unlock_irq(&pt->pt_irqfds_lock);
eventfd_ctx_put(eventfd);