Re: [PATCH v2 0/3] virtio: synchronize callbacks during device reset

On Sat, Sep 05, 2026 at 05:20:56PM +0200, Karl Mehltretter wrote:

A virtqueue callback can outlive virtio_reset_device() and race with a
driver freeing the state it uses. The reset helper documents that no
callbacks remain in progress, but that depends on the transport:
virtio-pci waits in vp_reset(), while virtio-mmio does not.

virtio_input has a related ordering problem: it unregisters the input
device before resetting the virtio device, while an event callback may
still be using the input device.

Patch 1 moves the callback wait into the core, using the existing
virtio_synchronize_cbs() operation. Patch 2 fixes the virtio_input teardown
order. Patch 3 adds the missing synchronize_cbs hooks for UML, TmFIFO,
remoteproc and virtio-vdpa. Remoteproc uses one SRCU domain per processor.

The new hooks wait for callbacks already running. UML, TmFIFO and
remoteproc still allow new callbacks after reset; fixing that is separate
work. The event-virtqueue DMA mapping issue is also separate.

Changes in v2:
- Patch 1: move the wait into the core instead of fixing only MMIO, as
  Michael suggested. Remove the duplicate PCI wait, preserve its shutdown
  wait, and fix CCW callback locking. Drop the MMIO polling: reset polling
  for v3 and newer is already in fa8833c085b6 ("virtio-mmio: add support
  for transport version 3").
- Patch 2: keep draining completed events when ready becomes false,
  instead of breaking out, so teardown does not truncate an input packet.
- Patch 3 is new, at Michael's request.

got all 3 patches now. it's a good start, thanks, but they need
a bit more work, in particular addressing sashiko comments.
I'd also prefer patch 1 to be split: moving code from pci to core
is separate from ccw fixes.

Pls write or at least edit commit log messages yourself,
after reviewing Documentation/process/coding-assistants.rst

Thanks a lot!

I reran the 120-cycle unbind/rebind test in an arm64 KASAN guest with four
vCPUs and a 5 ms busy delay per event. With patch 2 alone over virtio-mmio,
reset returned with the callback still running in all 84 overlapping
cycles. With the series, it waited in all 103. Over PCI with per-queue
MSI-X, it waited in all 66, including runs with threadirqs. No KASAN or
lockdep reports. These runs predate the per-rproc change, which leaves
the tested MMIO and PCI paths unchanged. They confirmed the missing wait,
but did not reproduce a use-after-free: with evdev attached,
input_unregister_device() waits for an RCU grace period that the IRQ
callback blocks.

That version also passed QEMU input, rebind and shutdown checks on arm64
MMIO and x86-64 PCI, including arm64 RT, KASAN and KCSAN builds, and x86
UP/Tiny SRCU. A legacy INTx NIC was present for an additional x86
shutdown check. The changed objects built with W=1 without warnings on
arm64, x86-64, s390 and SMP UML. The per-rproc version built with W=1
on arm64 KASAN and x86 Tiny SRCU, and passed six remoteproc callback and
lifetime KUnit tests on each, using mock remoteproc devices.

Link: https://lore.kernel.org/r/20260818040433.66986-1-kmehltretter@gmail.com (local)

Karl Mehltretter (3):
  virtio: synchronize callbacks during device reset
  virtio_input: stop callbacks before unregistering input device
  virtio: implement synchronize_cbs for remaining transports

 arch/um/drivers/virtio_uml.c             | 10 ++++++++++
 drivers/platform/mellanox/mlxbf-tmfifo.c | 14 ++++++++++++++
 drivers/remoteproc/remoteproc_core.c     | 10 ++++++++++
 drivers/remoteproc/remoteproc_virtio.c   | 20 +++++++++++++++++---
 drivers/s390/virtio/virtio_ccw.c         |  6 +-----
 drivers/virtio/virtio.c                  |  2 ++
 drivers/virtio/virtio_input.c            |  8 ++++++--
 drivers/virtio/virtio_pci_legacy.c       |  2 --
 drivers/virtio/virtio_pci_modern.c       |  3 ---
 drivers/virtio/virtio_vdpa.c             | 21 ++++++++++++++++++++-
 include/linux/remoteproc.h               |  3 +++
 include/linux/virtio_config.h            |  6 +++---
 12 files changed, 86 insertions(+), 19 deletions(-)

base-commit: a500db7819c50db59e55f1b4fa1c3baa5a2616f3
-- 
2.39.5 (Apple Git-154)