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xdp: document xdp_do_flush() before napi_complete_done()

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Document in the XDP_REDIRECT manual section that drivers must call
xdp_do_flush() before napi_complete_done(). The two reasons behind
this can be found following the links below.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.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/
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Magnus Karlsson 2023-01-17 10:43:05 +01:00 committed by David S. Miller
parent bed91ac081
commit 68e5b6aa27
1 changed files with 7 additions and 3 deletions
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10
net/core/filter.c
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@ -4128,9 +4128,13 @@ static const struct bpf_func_proto bpf_xdp_adjust_meta_proto = {
* bpf_redirect_info to actually enqueue the frame into a map type-specific
* bulk queue structure.
*
* 3. Before exiting its NAPI poll loop, the driver will call xdp_do_flush(),
* which will flush all the different bulk queues, thus completing the
* redirect.
* 3. Before exiting its NAPI poll loop, the driver will call
* xdp_do_flush(), which will flush all the different bulk queues,
* thus completing the redirect. Note that xdp_do_flush() must be
* called before napi_complete_done() in the driver, as the
* XDP_REDIRECT logic relies on being inside a single NAPI instance
* through to the xdp_do_flush() call for RCU protection of all
* in-kernel data structures.
*/
/*
* Pointers to the map entries will be kept around for this whole sequence of