From ad0ab027fc6da08cbd34070d816ff3b7986c64ae Mon Sep 17 00:00:00 2001 From: Jesper Dangaard Brouer Date: Wed, 8 Aug 2018 23:00:34 +0200 Subject: xdp: fix bug in cpumap teardown code path When removing a cpumap entry, a number of syncronization steps happen. Eventually the teardown code __cpu_map_entry_free is invoked from/via call_rcu. The teardown code __cpu_map_entry_free() flushes remaining xdp_frames, by invoking bq_flush_to_queue, which calls xdp_return_frame_rx_napi(). The issues is that the teardown code is not running in the RX NAPI code path. Thus, it is not allowed to invoke the NAPI variant of xdp_return_frame. This bug was found and triggered by using the --stress-mode option to the samples/bpf program xdp_redirect_cpu. It is hard to trigger, because the ptr_ring have to be full and cpumap bulk queue max contains 8 packets, and a remote CPU is racing to empty the ptr_ring queue. Fixes: 389ab7f01af9 ("xdp: introduce xdp_return_frame_rx_napi") Tested-by: Jean-Tsung Hsiao Signed-off-by: Jesper Dangaard Brouer Signed-off-by: Daniel Borkmann --- kernel/bpf/cpumap.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c index e0918d180f08..46f5f29605d4 100644 --- a/kernel/bpf/cpumap.c +++ b/kernel/bpf/cpumap.c @@ -69,7 +69,7 @@ struct bpf_cpu_map { }; static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu, - struct xdp_bulk_queue *bq); + struct xdp_bulk_queue *bq, bool in_napi_ctx); static u64 cpu_map_bitmap_size(const union bpf_attr *attr) { @@ -375,7 +375,7 @@ static void __cpu_map_entry_free(struct rcu_head *rcu) struct xdp_bulk_queue *bq = per_cpu_ptr(rcpu->bulkq, cpu); /* No concurrent bq_enqueue can run at this point */ - bq_flush_to_queue(rcpu, bq); + bq_flush_to_queue(rcpu, bq, false); } free_percpu(rcpu->bulkq); /* Cannot kthread_stop() here, last put free rcpu resources */ @@ -558,7 +558,7 @@ const struct bpf_map_ops cpu_map_ops = { }; static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu, - struct xdp_bulk_queue *bq) + struct xdp_bulk_queue *bq, bool in_napi_ctx) { unsigned int processed = 0, drops = 0; const int to_cpu = rcpu->cpu; @@ -578,7 +578,10 @@ static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu, err = __ptr_ring_produce(q, xdpf); if (err) { drops++; - xdp_return_frame_rx_napi(xdpf); + if (likely(in_napi_ctx)) + xdp_return_frame_rx_napi(xdpf); + else + xdp_return_frame(xdpf); } processed++; } @@ -598,7 +601,7 @@ static int bq_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_frame *xdpf) struct xdp_bulk_queue *bq = this_cpu_ptr(rcpu->bulkq); if (unlikely(bq->count == CPU_MAP_BULK_SIZE)) - bq_flush_to_queue(rcpu, bq); + bq_flush_to_queue(rcpu, bq, true); /* Notice, xdp_buff/page MUST be queued here, long enough for * driver to code invoking us to finished, due to driver @@ -661,7 +664,7 @@ void __cpu_map_flush(struct bpf_map *map) /* Flush all frames in bulkq to real queue */ bq = this_cpu_ptr(rcpu->bulkq); - bq_flush_to_queue(rcpu, bq); + bq_flush_to_queue(rcpu, bq, true); /* If already running, costs spin_lock_irqsave + smb_mb */ wake_up_process(rcpu->kthread); -- cgit v1.2.3