Re: [PATCH v3 0/5] nvdimm: virtio_pmem: fix request lifetime and converge broken queue failures

[Alison Schofield]

On Thu, Feb 26, 2026 at 10:57:05AM +0800, Li Chen wrote:
> Hi,
> 
> The virtio-pmem flush path uses a virtqueue cookie/token to carry a
> per-request context through completion. Under broken virtqueue / notify
> failure conditions, the submitter can return and free the request object
> while the host/backend may still complete the published request. The IRQ
> completion handler then dereferences freed memory when waking waiters,
> which is reported by KASAN as a slab-use-after-free and may manifest as
> lock corruption (e.g. "BUG: spinlock already unlocked") without KASAN.
> 
> In addition, the flush path has two wait sites: one for virtqueue
> descriptor availability (-ENOSPC from virtqueue_add_sgs()) and one for
> request completion. If the virtqueue becomes broken, forward progress is
> no longer guaranteed and these waiters may sleep indefinitely unless the
> driver converges the failure and wakes all wait sites.
> 
> This series addresses both issues:
> 
> 1/5 nvdimm: virtio_pmem: always wake -ENOSPC waiters
> Wake one -ENOSPC waiter for each reclaimed used buffer, decoupled from
> token completion.
> 
> 2/5 nvdimm: virtio_pmem: use READ_ONCE()/WRITE_ONCE() for wait flags
> Use READ_ONCE()/WRITE_ONCE() for the wait_event() flags (done and
> wq_buf_avail).
> 
> 3/5 nvdimm: virtio_pmem: refcount requests for token lifetime
> Refcount request objects so the token lifetime spans the window where it
> is reachable through the virtqueue until completion/drain drops the
> virtqueue reference.
> 
> 4/5 nvdimm: virtio_pmem: converge broken virtqueue to -EIO
> Track a device-level broken state to converge broken/notify failures to
> -EIO: wake all waiters and drain/detach outstanding requests to complete
> them with an error, and fail-fast new requests.
> 
> 5/5 nvdimm: virtio_pmem: drain requests in freeze
> Drain outstanding requests in freeze() before tearing down virtqueues so
> waiters do not sleep indefinitely.
> 
> Testing was done on QEMU x86_64 with a virtio-pmem device exported as
> /dev/pmem0, formatted with ext4 (-O fast_commit), mounted with DAX, and
> stressed with fsync-heavy workloads.
> 
> Thanks,
> Li Chen

Hi Li Chen,

Today I took a look at this set, noting that it's been sitting idle 
in our nvdimm backlog for a while. I'm not able to apply it. Can you
post a new rev that applies to 7.1-rc6 ?

Thanks,
Alison