net: 8139cp: keep Rx masked while NAPI is scheduled

cp_rx_poll() calls napi_complete_done() and only then takes cp->lock
with interrupts disabled to unmask the Rx interrupts. An interrupt
that is not masked while polling (TxOK, TxErr, ...) can arrive in
between. cp_interrupt() then sees the Rx status bits, which are still
set, finds NAPI no longer scheduled, masks Rx and schedules NAPI again.
cp_rx_poll() then carries on and unmasks Rx anyway.

From that point Rx interrupts are enabled while NAPI is scheduled:
cp_interrupt() leaves the Rx bits for the poll routine, does not mask
them because napi_schedule_prep() fails, and the level-triggered
interrupt fires again as soon as it returns. On an SH7751 LANDISK
under combined Tx/Rx load this interrupt storm was captured with a RAM
trace right before the board locked up hard.

Mask Rx in cp_interrupt() whenever Rx status is pending, not only when
NAPI gets scheduled. If the race leaves Rx unmasked, the next interrupt
masks it again, and the pending poll unmasks it when it completes.

Fixes: ab1e7e1d2666 ("8139cp: use napi_complete_done()")
Signed-off-by: Colton Pawielski <colton.pawielski@gmail.com>
Reviewed-by: Daniel Machon <daniel.machon@microchip.com>
Link: https://patch.msgid.link/20261031-b4-8139cp-napi-v2-1-5824797c0fe6@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

0 files changed, 0 insertions, 0 deletions