[PATCH] event/dsw: fix migration bug

[Thomas Monjalon]

11/07/2022 14:45, Jerin Jacob:
> On Thu, Jul 7, 2022 at 5:13 PM Mattias Rönnblom <hofors at lysator.liu.se> wrote:
> >
> > From: Mattias Rönnblom <mattias.ronnblom at ericsson.com>
> >
> > Fix bug in flow migration, which under certain conditions causes
> > reordering and violation of atomicity guarantees.
> >
> > The issue occurs when the processing of a flow (on an atomic queue)
> > has resulted in events enqueued to a flow currently being migrated,
> > and the former (producer) flow is also selected for migration. The
> > events are buffered ("paused") on the originating port, and released
> > (forwarded) when the migration has completed. However, at the time of
> > "unpausing" the latter (consumer) flow, processing of the producer
> > flow on the port to which it was migrated may have already produced
> > events, for the same paused flow. This constitutes a race condition,
> > and depending on which port wins, reordering may have been introduced.
> >
> > This patch forbids migration when a port has paused events, since
> > those events may have been the result of processing a to-be-migrated
> > flow.
> >
> > This patch also disallows processing events pertaining to a flow under
> > migration, for the same reason. A new buffer is introduced, which
> > holds such not-yet-processed events dequeued from the port's input
> > ring. Such events are forwarded to the target port as a part of the
> > migration process.
> >
> > The 'forwarding' migration state is eliminated, and instead background
> > processing is only performed if there are no unreleased events on the
> > port.
> >
> > The bug is primarily triggered in situations where multiple flows are
> > migrated as one transaction, but may occur even if only a single flow
> > is migrated (e.g., with older DSW versions, which does not support
> > multi-flow migration).
> >
> > Fixes: f6257b22e767 ("event/dsw: add load balancing")
> > Cc: stable at dpdk.org
> >
> > Signed-off-by: Mattias Rönnblom <mattias.ronnblom at ericsson.com>
> 
> + @Thomas Monjalon  to merge to the main tree directly.

No sorry,
it would not be serious to merge such a big patch in the last minute.
And it is not a new bug.