On 06/01/2019 12:37 AM, Matt Mullins wrote:
> It is possible that a BPF program can be called while another BPF
> program is executing bpf_perf_event_output. This has been observed with
> I/O completion occurring as a result of an interrupt:
>
> bpf_prog_247fd1341cddaea4_trace_req_end+0x8d7/0x1000
> ? trace_call_bpf+0x82/0x100
> ? sch_direct_xmit+0xe2/0x230
> ? blk_mq_end_request+0x1/0x100
> ? blk_mq_end_request+0x5/0x100
> ? kprobe_perf_func+0x19b/0x240
> ? __qdisc_run+0x86/0x520
> ? blk_mq_end_request+0x1/0x100
> ? blk_mq_end_request+0x5/0x100
> ? kprobe_ftrace_handler+0x90/0xf0
> ? ftrace_ops_assist_func+0x6e/0xe0
> ? ip6_input_finish+0xbf/0x460
> ? 0xffffffffa01e80bf
> ? nbd_dbg_flags_show+0xc0/0xc0 [nbd]
> ? blkdev_issue_zeroout+0x200/0x200
> ? blk_mq_end_request+0x1/0x100
> ? blk_mq_end_request+0x5/0x100
> ? flush_smp_call_function_queue+0x6c/0xe0
> ? smp_call_function_single_interrupt+0x32/0xc0
> ? call_function_single_interrupt+0xf/0x20
> ? call_function_single_interrupt+0xa/0x20
> ? swiotlb_map_page+0x140/0x140
> ? refcount_sub_and_test+0x1a/0x50
> ? tcp_wfree+0x20/0xf0
> ? skb_release_head_state+0x62/0xc0
> ? skb_release_all+0xe/0x30
> ? napi_consume_skb+0xb5/0x100
> ? mlx5e_poll_tx_cq+0x1df/0x4e0
> ? mlx5e_poll_tx_cq+0x38c/0x4e0
> ? mlx5e_napi_poll+0x58/0xc30
> ? mlx5e_napi_poll+0x232/0xc30
> ? net_rx_action+0x128/0x340
> ? __do_softirq+0xd4/0x2ad
> ? irq_exit+0xa5/0xb0
> ? do_IRQ+0x7d/0xc0
> ? common_interrupt+0xf/0xf
> </IRQ>
> ? __rb_free_aux+0xf0/0xf0
> ? perf_output_sample+0x28/0x7b0
> ? perf_prepare_sample+0x54/0x4a0
> ? perf_event_output+0x43/0x60
> ? bpf_perf_event_output_raw_tp+0x15f/0x180
> ? blk_mq_start_request+0x1/0x120
> ? bpf_prog_411a64a706fc6044_should_trace+0xad4/0x1000
> ? bpf_trace_run3+0x2c/0x80
> ? nbd_send_cmd+0x4c2/0x690 [nbd]
>
> This also cannot be alleviated by further splitting the per-cpu
> perf_sample_data structs (as in commit 283ca526a9bd ("bpf: fix
> corruption on concurrent perf_event_output calls")), as a raw_tp could
> be attached to the block:block_rq_complete tracepoint and execute during
> another raw_tp. Instead, keep a pre-allocated perf_sample_data
> structure per perf_event_array element and fail a bpf_perf_event_output
> if that element is concurrently being used.
>
> Fixes: 20b9d7ac4852 ("bpf: avoid excessive stack usage for perf_sample_data")
> Signed-off-by: Matt Mullins <mmullins@xxxxxx>
You do not elaborate why is this needed for all the networking programs that
use this functionality. The bpf_misc_sd should therefore be kept as-is. There
cannot be nested occurrences there (xdp, tc ingress/egress). Please explain why
non-tracing should be affected here...
