From: John Fastabend <john.fastabend@gmail.com>
To: bjorn.topel@gmail.com, bpf@vger.kernel.org, toke@redhat.com,
toshiaki.makita1@gmail.com
Cc: netdev@vger.kernel.org, john.fastabend@gmail.com, ast@kernel.org,
daniel@iogearbox.net
Subject: [bpf-next PATCH v2 1/2] bpf: xdp, update devmap comments to reflect napi/rcu usage
Date: Sat, 11 Jan 2020 18:37:21 -0800 [thread overview]
Message-ID: <157879664156.8200.4955971883120344808.stgit@john-Precision-5820-Tower> (raw)
In-Reply-To: <157879606461.8200.2816751890292483534.stgit@john-Precision-5820-Tower>
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")
Acked-by: Björn Töpel <bjorn.topel@intel.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
kernel/bpf/devmap.c | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)
diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index da9c832..f0bf525 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -193,10 +193,12 @@ static void dev_map_free(struct bpf_map *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 relavent 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);
@@ -498,12 +500,11 @@ static int dev_map_delete_elem(struct bpf_map *map, void *key)
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)
next prev parent reply other threads:[~2020-01-12 2:37 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-12 2:36 [bpf-next PATCH v2 0/2] xdp devmap improvements cleanup John Fastabend
2020-01-12 2:37 ` John Fastabend [this message]
2020-01-12 7:47 ` [bpf-next PATCH v2 1/2] bpf: xdp, update devmap comments to reflect napi/rcu usage Maciej Fijalkowski
2020-01-14 3:27 ` John Fastabend
2020-01-12 11:21 ` Toke Høiland-Jørgensen
2020-01-12 2:37 ` [bpf-next PATCH v2 2/2] bpf: xdp, remove no longer required rcu_read_{un}lock() John Fastabend
2020-01-12 6:49 ` Maciej Fijalkowski
2020-01-14 3:25 ` John Fastabend
2020-01-14 0:31 ` Maciej Fijalkowski
2020-01-12 11:22 ` Toke Høiland-Jørgensen
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