Re: [PATCH v3 0/6] virtio: fix and add callback synchronization hooks

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Sep 08, 2026 at 07:38:11AM +0200, Karl Mehltretter wrote:
> This is v3 of the callback synchronization series. It is based on
> Michael S. Tsirkin's linux-next branch at f49e6cf91942 ("virtio:
> synchronize callbacks after device reset"), which already contains the
> core change and the virtio_input teardown reorder from v2.


Thanks I applied since this looks like a net improvement.
Pls keep iterating on the core change.
If you want to take a stab at some of the pre-existing issues -
will be welcome.
Pls do note which patches were tested and which were not.

> Patches 1 and 2 fix two bugs in virtio-ccw's existing
> synchronize_cbs() hook. After a fallback from adapter to classic
> interrupts it selects the wrong lock, and the classic interrupt handler
> only takes the matching lock when notification hardening is enabled.
> Patch 3 adds SRCU tracking for remoteproc callbacks, which can sleep.
> Patches 4 and 5 replace the RCU fallback with synchronization against
> the UML IRQ and the TmFIFO callback locks. The fallback already covers
> these IRQ handlers and spinlock sections. Patch 6 adds SRCU tracking
> in virtio_vdpa so callback synchronization does not depend on the
> context in which the vDPA driver invokes the callback.
> 
> The UML, TmFIFO and remoteproc reset paths do not themselves prevent
> new virtqueue callbacks. UML and TmFIFO only clear a status field, and
> remoteproc does not wait for the remote side to acknowledge the reset.
> Without notification hardening or driver-specific teardown protection,
> callbacks can still start after reset. The new synchronization hooks
> do not fix that. The TmFIFO hook also does not synchronize with the
> rest of the FIFO work item outside the callback locks.
> 
> The virtio_input loop change from v2 (continue instead of break, so
> events the device already completed are still delivered) and the
> event buffer leak are sent separately.
> 
> Changes in v3:
> - Rebased on Michael's linux-next branch. Dropped the core change and
>   the virtio_input patch, which are there already.
> - Split the virtio-ccw fixes out of the core patch, one per bug, and
>   the transport patch into one patch per transport. The CCW and TmFIFO
>   changes are functionally unchanged from v2.
> - Patch 2: added a Fixes tag and described the existing shutdown
>   case. Removed the dependency note on the core reset change.
> - remoteproc: read the queue pointer once in rproc_vq_interrupt(), and
>   synchronize with callbacks in __rproc_virtio_del_vqs() before
>   freeing the queues (Sashiko). Place vq_srcu next to rvdevs so the
>   hunk also applies to mainline, which added attach_work after index.
> - virtio_uml: compare against UM_IRQ_ALLOC instead of a bare negative
>   check.
> - virtio_vdpa: use SRCU instead of a per-device rwlock, so the
>   callback tracking uses per-CPU counters, and cover the config
>   callback (Sashiko).
> - Rewrote the commit messages. Corrected the RCU fallback description
>   for UML, TmFIFO and the vDPA simulators. Dropped the claimed simulator
>   reset race: the simulators disable bottom halves around virtqueue
>   callbacks and serialize reset with the worker's mutex.
> 
> Changes in v2:
> - Moved callback synchronization from virtio-pci into the core, as
>   Michael suggested, and added the missing synchronize_cbs() hooks.
> 
> Testing: the changed objects build with W=1 without warnings, with
> clang on arm64, x86-64 and s390 and with gcc on SMP UML, and the
> patches also apply to current mainline and linux-next. The runtime
> tests from v2 were not repeated on this version: the input, rebind and
> shutdown checks on arm64 MMIO and x86 PCI covered code that is
> unchanged here, and the remoteproc and virtio_vdpa hooks have only
> been build-tested. No remoteproc, TmFIFO or s390 hardware was
> available.
> 
> v2: https://lore.kernel.org/r/20260905152059.89560-1-kmehltretter@gmail.com
> v1: https://lore.kernel.org/r/20260818040433.66986-1-kmehltretter@gmail.com
> 
> Karl Mehltretter (6):
>   virtio_ccw: fix synchronize_cbs() after interrupt fallback
>   virtio_ccw: always take irq_lock in the classic interrupt handler
>   remoteproc: implement synchronize_cbs() for virtio devices
>   um: virtio_uml: implement synchronize_cbs()
>   platform/mellanox: mlxbf-tmfifo: implement synchronize_cbs()
>   virtio_vdpa: implement synchronize_cbs()
> 
>  arch/um/drivers/virtio_uml.c             | 10 +++++++
>  drivers/platform/mellanox/mlxbf-tmfifo.c | 15 ++++++++++
>  drivers/remoteproc/remoteproc_core.c     | 12 ++++++++
>  drivers/remoteproc/remoteproc_virtio.c   | 37 +++++++++++++++++++-----
>  drivers/s390/virtio/virtio_ccw.c         |  6 +---
>  drivers/virtio/virtio_vdpa.c             | 34 ++++++++++++++++++++--
>  include/linux/remoteproc.h               |  3 ++
>  7 files changed, 102 insertions(+), 15 deletions(-)
> 
> 
> base-commit: f49e6cf919425cc55f10fd7cda7e0fc895df4cc0
> -- 
> 2.39.5 (Apple Git-154)