On Thu, 2019-05-30 at 23:28 +0000, Song Liu wrote: > > On May 30, 2019, at 3:55 PM, Matt Mullins <mmullins@xxxxxx> 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> > > --- > > 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; > }; Yeah, that totally works. I was mostly doing this so we had only one kmalloc allocation, but I'm not too worried about having an extra object in kmalloc-64 if it simplifies the code a lot. > > > -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? You mean xchg a null-pointer or something in there while it's in-use, then xchg the slab back? Makes sense to me. I'll try that and see where it gets me. > > 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 > > > >