Re: [PATCH v2 5/6] cxl/port: Prevent out-of-order decoder allocation

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Tue, 22 Oct 2024 18:43:57 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> With the recent change to allow out-of-order decoder de-commit it
> highlights a need to strengthen the in-order decoder commit guarantees.
> As it stands match_free_decoder() ensures that if 2 regions are racing
> decoder allocations the one that wins the race will get the lower id
> decoder, but that still leaves the race to *commit* the decoder.
> 
> Rather than have this complicated case of "reserved in-order, but may
> still commit out-of-order", just arrange for the reservation order to
> match the commit-order. In other words, prevent subsequent allocations
> until the last reservation is committed.
> 
> This precludes overlapping region creation events and requires the
> previous regionN to either move forward to the decoder commit stage or
> drop its reservation before regionN+1 can move forward. That is,
> provided that regionN and regionN+1 decode through the same switch port.
> 
> As a side effect this allows match_free_decoder() to drop its dependency
> on needing write access to the device_find_child() @data parameter [1].
> 
> Reported-by: Zijun Hu <quic_zijuhu@quicinc.com>
> Closes: http://lore.kernel.org/20240905-const_dfc_prepare-v4-0-4180e1d5a244@quicinc.com
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: Vishal Verma <vishal.l.verma@intel.com>
> Cc: Alison Schofield <alison.schofield@intel.com>
> Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
LGTM
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>