From: John Fastabend <john.fastabend@gmail.com>
To: bjorn.topel@gmail.com, bpf@vger.kernel.org, toke@redhat.com
Cc: netdev@vger.kernel.org, john.fastabend@gmail.com, ast@kernel.org,
daniel@iogearbox.net
Subject: [bpf PATCH 2/2] bpf: xdp, remove no longer required rcu_read_{un}lock()
Date: Wed, 08 Jan 2020 13:35:06 -0800 [thread overview]
Message-ID: <157851930654.21459.7236323146782270917.stgit@john-Precision-5820-Tower> (raw)
In-Reply-To: <157851907534.21459.1166135254069483675.stgit@john-Precision-5820-Tower>
Now that we depend on rcu_call() and synchronize_rcu() to also wait
for preempt_disabled region to complete the rcu read critical section
in __dev_map_flush() is no longer relevant.
These originally ensured the map reference was safe while a map was
also being free'd. But flush by new rules can only be called from
preempt-disabled NAPI context. The synchronize_rcu from the map free
path and the rcu_call from the delete path will ensure the reference
here is safe. So lets remove the rcu_read_lock and rcu_read_unlock
pair to avoid any confusion around how this is being protected.
If the rcu_read_lock was required it would mean errors in the above
logic and the original patch would also be wrong.
Fixes: 0536b85239b84 ("xdp: Simplify devmap cleanup")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
kernel/bpf/devmap.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index f0bf525..0129d4a 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -378,10 +378,8 @@ void __dev_map_flush(void)
struct list_head *flush_list = this_cpu_ptr(&dev_map_flush_list);
struct xdp_bulk_queue *bq, *tmp;
- rcu_read_lock();
list_for_each_entry_safe(bq, tmp, flush_list, flush_node)
bq_xmit_all(bq, XDP_XMIT_FLUSH);
- rcu_read_unlock();
}
/* rcu_read_lock (from syscall and BPF contexts) ensures that if a delete and/or
next prev parent reply other threads:[~2020-01-08 21:35 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-08 21:34 [bpf PATCH 0/2] xdp devmap improvements cleanup John Fastabend
2020-01-08 21:34 ` [bpf PATCH 1/2] bpf: xdp, update devmap comments to reflect napi/rcu usage John Fastabend
2020-01-09 1:20 ` Song Liu
2020-01-08 21:35 ` John Fastabend [this message]
2020-01-09 1:21 ` [bpf PATCH 2/2] bpf: xdp, remove no longer required rcu_read_{un}lock() Song Liu
2020-01-09 6:01 ` Toshiaki Makita
2020-01-09 6:34 ` Toshiaki Makita
2020-01-09 6:35 ` John Fastabend
2020-01-09 6:57 ` Toshiaki Makita
2020-01-09 14:58 ` John Fastabend
2020-01-09 6:09 ` [bpf PATCH 0/2] xdp devmap improvements cleanup Björn Töpel
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