5.4-stable review patch. If anyone has any objections, please let me know.
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From: John Fastabend john.fastabend@gmail.com
commit 42a84a8cd0ff0cbff5a4595e1304c4567a30267d upstream.
Now that we rely on synchronize_rcu and call_rcu waiting to exit perempt-disable regions (NAPI) lets update the comments to reflect this.
Fixes: 0536b85239b84 ("xdp: Simplify devmap cleanup") Signed-off-by: John Fastabend john.fastabend@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Björn Töpel bjorn.topel@intel.com Acked-by: Song Liu songliubraving@fb.com Link: https://lore.kernel.org/bpf/1580084042-11598-2-git-send-email-john.fastabend... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/bpf/devmap.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-)
--- a/kernel/bpf/devmap.c +++ b/kernel/bpf/devmap.c @@ -210,10 +210,12 @@ static void dev_map_free(struct bpf_map
/* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0, * so the programs (can be more than one that used this map) were - * disconnected from events. Wait for outstanding critical sections in - * these programs to complete. The rcu critical section only guarantees - * no further reads against netdev_map. It does __not__ ensure pending - * flush operations (if any) are complete. + * disconnected from events. The following synchronize_rcu() guarantees + * both rcu read critical sections complete and waits for + * preempt-disable regions (NAPI being the relevant context here) so we + * are certain there will be no further reads against the netdev_map and + * all flush operations are complete. Flush operations can only be done + * from NAPI context for this reason. */
spin_lock(&dev_map_lock); @@ -518,12 +520,11 @@ static int dev_map_delete_elem(struct bp return -EINVAL;
/* Use call_rcu() here to ensure any rcu critical sections have - * completed, but this does not guarantee a flush has happened - * yet. Because driver side rcu_read_lock/unlock only protects the - * running XDP program. However, for pending flush operations the - * dev and ctx are stored in another per cpu map. And additionally, - * the driver tear down ensures all soft irqs are complete before - * removing the net device in the case of dev_put equals zero. + * completed as well as any flush operations because call_rcu + * will wait for preempt-disable region to complete, NAPI in this + * context. And additionally, the driver tear down ensures all + * soft irqs are complete before removing the net device in the + * case of dev_put equals zero. */ old_dev = xchg(&dtab->netdev_map[k], NULL); if (old_dev)