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qede: execute xdp_do_flush() before napi_complete_done()

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Make sure that xdp_do_flush() is always executed before
napi_complete_done(). This is important for two reasons. First, a
redirect to an XSKMAP assumes that a call to xdp_do_redirect() from
napi context X on CPU Y will be followed by a xdp_do_flush() from the
same napi context and CPU. This is not guaranteed if the
napi_complete_done() is executed before xdp_do_flush(), as it tells
the napi logic that it is fine to schedule napi context X on another
CPU. Details from a production system triggering this bug using the
veth driver can be found following the first link below.

The second reason is that the XDP_REDIRECT logic in itself relies on
being inside a single NAPI instance through to the xdp_do_flush() call
for RCU protection of all in-kernel data structures. Details can be
found in the second link below.

Fixes: d1b25b79e1 ("qede: add .ndo_xdp_xmit() and XDP_REDIRECT support")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20221220185903.1105011-1-sbohrer@cloudflare.com
Link: https://lore.kernel.org/all/20210624160609.292325-1-toke@redhat.com/
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Magnus Karlsson 2023-01-25 08:48:57 +01:00 committed by Jakub Kicinski
parent 28b4387f0e
commit 2ccce20d51
1 changed files with 4 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
drivers/net/ethernet/qlogic/qede/qede_fp.c
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@ -1438,6 +1438,10 @@ int qede_poll(struct napi_struct *napi, int budget)
rx_work_done = (likely(fp->type & QEDE_FASTPATH_RX) &&
qede_has_rx_work(fp->rxq)) ?
qede_rx_int(fp, budget) : 0;
if (fp->xdp_xmit & QEDE_XDP_REDIRECT)
xdp_do_flush();
/* Handle case where we are called by netpoll with a budget of 0 */
if (rx_work_done < budget || !budget) {
if (!qede_poll_is_more_work(fp)) {
@ -1457,9 +1461,6 @@ int qede_poll(struct napi_struct *napi, int budget)
qede_update_tx_producer(fp->xdp_tx);
}
if (fp->xdp_xmit & QEDE_XDP_REDIRECT)
xdp_do_flush_map();
return rx_work_done;
}