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Date: Thu, 30 May 2019 23:28:14 +0000
From: Song Liu <songliubraving@...com>
To: Matt Mullins <mmullins@...com>
CC: Andrew Hall <hall@...com>, Alexei Starovoitov <ast@...nel.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Martin Lau <kafai@...com>, Yonghong Song <yhs@...com>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH bpf] bpf: preallocate a perf_sample_data per event fd
> On May 30, 2019, at 3:55 PM, Matt Mullins <mmullins@...com> 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@...com>
> ---
> It felt a bit overkill, but I had to split bpf_event_entry into its own
> header file to break an include cycle from perf_event.h -> cgroup.h ->
> cgroup-defs.h -> bpf-cgroup.h -> bpf.h -> (potentially) perf_event.h.
>
> include/linux/bpf.h | 7 -------
> include/linux/bpf_event.h | 20 ++++++++++++++++++++
> kernel/bpf/arraymap.c | 2 ++
> kernel/trace/bpf_trace.c | 30 +++++++++++++++++-------------
> 4 files changed, 39 insertions(+), 20 deletions(-)
> create mode 100644 include/linux/bpf_event.h
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 4fb3aa2dc975..13b253a36402 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -467,13 +467,6 @@ static inline bool bpf_map_flags_access_ok(u32 access_flags)
> (BPF_F_RDONLY_PROG | BPF_F_WRONLY_PROG);
> }
>
I think we can avoid the include cycle as:
+struct perf_sample_data *sd;
struct bpf_event_entry {
struct perf_event *event;
struct file *perf_file;
struct file *map_file;
struct rcu_head rcu;
+ struct perf_sample_data *sd;
};
> -struct bpf_event_entry {
> - struct perf_event *event;
> - struct file *perf_file;
> - struct file *map_file;
> - struct rcu_head rcu;
> -};
> -
> bool bpf_prog_array_compatible(struct bpf_array *array, const struct bpf_prog *fp);
> int bpf_prog_calc_tag(struct bpf_prog *fp);
>
> diff --git a/include/linux/bpf_event.h b/include/linux/bpf_event.h
> new file mode 100644
> index 000000000000..9f415990f921
> --- /dev/null
> +++ b/include/linux/bpf_event.h
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _LINUX_BPF_EVENT_H
> +#define _LINUX_BPF_EVENT_H
> +
> +#include <linux/perf_event.h>
> +#include <linux/types.h>
> +
> +struct file;
> +
> +struct bpf_event_entry {
> + struct perf_event *event;
> + struct file *perf_file;
> + struct file *map_file;
> + struct rcu_head rcu;
> + struct perf_sample_data sd;
> + atomic_t in_use;
> +};
> +
> +#endif /* _LINUX_BPF_EVENT_H */
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 584636c9e2eb..08e5e486d563 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -11,6 +11,7 @@
> * General Public License for more details.
> */
> #include <linux/bpf.h>
> +#include <linux/bpf_event.h>
> #include <linux/btf.h>
> #include <linux/err.h>
> #include <linux/slab.h>
> @@ -659,6 +660,7 @@ static struct bpf_event_entry *bpf_event_entry_gen(struct file *perf_file,
> ee->event = perf_file->private_data;
> ee->perf_file = perf_file;
> ee->map_file = map_file;
And do the kzalloc() or some other trick here.
> + atomic_set(&ee->in_use, 0);
> }
>
> return ee;
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index f92d6ad5e080..a03e29957698 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -6,6 +6,7 @@
> #include <linux/types.h>
> #include <linux/slab.h>
> #include <linux/bpf.h>
> +#include <linux/bpf_event.h>
> #include <linux/bpf_perf_event.h>
> #include <linux/filter.h>
> #include <linux/uaccess.h>
> @@ -410,17 +411,17 @@ static const struct bpf_func_proto bpf_perf_event_read_value_proto = {
> .arg4_type = ARG_CONST_SIZE,
> };
>
> -static DEFINE_PER_CPU(struct perf_sample_data, bpf_trace_sd);
> -
> static __always_inline u64
> __bpf_perf_event_output(struct pt_regs *regs, struct bpf_map *map,
> - u64 flags, struct perf_sample_data *sd)
> + u64 flags, struct perf_raw_record *raw)
> {
> struct bpf_array *array = container_of(map, struct bpf_array, map);
> unsigned int cpu = smp_processor_id();
> u64 index = flags & BPF_F_INDEX_MASK;
> struct bpf_event_entry *ee;
> struct perf_event *event;
> + struct perf_sample_data *sd;
> + u64 ret;
>
> if (index == BPF_F_CURRENT_CPU)
> index = cpu;
> @@ -439,13 +440,22 @@ __bpf_perf_event_output(struct pt_regs *regs, struct bpf_map *map,
> if (unlikely(event->oncpu != cpu))
> return -EOPNOTSUPP;
>
> - return perf_event_output(event, sd, regs);
> + if (atomic_cmpxchg(&ee->in_use, 0, 1) != 0)
> + return -EBUSY;
And we only need xchg() here, so we can eliminate in_use.
Does this make sense?
Thanks,
Song
> +
> + sd = &ee->sd;
> + perf_sample_data_init(sd, 0, 0);
> + sd->raw = raw;
> +
> + ret = perf_event_output(event, sd, regs);
> +
> + atomic_set(&ee->in_use, 0);
> + return ret;
> }
>
> BPF_CALL_5(bpf_perf_event_output, struct pt_regs *, regs, struct bpf_map *, map,
> u64, flags, void *, data, u64, size)
> {
> - struct perf_sample_data *sd = this_cpu_ptr(&bpf_trace_sd);
> struct perf_raw_record raw = {
> .frag = {
> .size = size,
> @@ -456,10 +466,8 @@ BPF_CALL_5(bpf_perf_event_output, struct pt_regs *, regs, struct bpf_map *, map,
> if (unlikely(flags & ~(BPF_F_INDEX_MASK)))
> return -EINVAL;
>
> - perf_sample_data_init(sd, 0, 0);
> - sd->raw = &raw;
>
> - return __bpf_perf_event_output(regs, map, flags, sd);
> + return __bpf_perf_event_output(regs, map, flags, &raw);
> }
>
> static const struct bpf_func_proto bpf_perf_event_output_proto = {
> @@ -474,12 +482,10 @@ static const struct bpf_func_proto bpf_perf_event_output_proto = {
> };
>
> static DEFINE_PER_CPU(struct pt_regs, bpf_pt_regs);
> -static DEFINE_PER_CPU(struct perf_sample_data, bpf_misc_sd);
>
> u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
> void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy)
> {
> - struct perf_sample_data *sd = this_cpu_ptr(&bpf_misc_sd);
> struct pt_regs *regs = this_cpu_ptr(&bpf_pt_regs);
> struct perf_raw_frag frag = {
> .copy = ctx_copy,
> @@ -497,10 +503,8 @@ u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
> };
>
> perf_fetch_caller_regs(regs);
> - perf_sample_data_init(sd, 0, 0);
> - sd->raw = &raw;
>
> - return __bpf_perf_event_output(regs, map, flags, sd);
> + return __bpf_perf_event_output(regs, map, flags, &raw);
> }
>
> BPF_CALL_0(bpf_get_current_task)
> --
> 2.17.1
>
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