Re: [RFC PATCH 06/19] vfio/pci: Serialize ioeventfd writes with recovery

[sashiko-bot@kernel.org]

> Share one write helper between the ioeventfd fast path and the threaded
> one. It takes memory_lock, checks the recovery state, then writes. The
> fast path runs from the virqfd wakeup with a spinlock held, so it
> trylocks and hands off to the thread if the lock is busy. The thread can
> block.
> 
> The ioeventfd write path must not take recovery_lock at all. It is
> reached through flush_work() from the virqfd cleanup workqueue, and
> VFIO_DEVICE_SET_IRQS later calls vfio_virqfd_disable(), which does that
> flush while holding recovery_lock for reading. If the write then blocked
> on recovery_lock behind a queued AER writer, all three would be stuck.
> The flush waits for the write, the write waits for the AER writer, and
> the AER writer waits for the reader driving the flush.
> 
> So the recovery state is read lock-free, and the write goes through the
> [ ... ]
> live, so testing it unconditionally would drop every ioeventfd write for
> every other vfio-pci-core driver.
> 
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260901093217.8539-1-skolothumtho@nvidia.com?part=6