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 <[email protected]>
---
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);
}
-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;
+ 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;
+
+ 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
> On May 30, 2019, at 3:55 PM, Matt Mullins <[email protected]> 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 <[email protected]>
> ---
> 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
>
On Thu, 2019-05-30 at 23:28 +0000, Song Liu wrote:
> > On May 30, 2019, at 3:55 PM, Matt Mullins <[email protected]> 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 <[email protected]>
> > ---
> > 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
> >
>
>
> On May 30, 2019, at 5:01 PM, Matt Mullins <[email protected]> wrote:
>
> On Thu, 2019-05-30 at 23:28 +0000, Song Liu wrote:
>>> On May 30, 2019, at 3:55 PM, Matt Mullins <[email protected]> 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 <[email protected]>
>>> ---
>>> 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.
We can also do something like
ee = kzalloc(sizeof(struct bpf_event_entry) + sizeof(struct perf_sample_data));
ee->sd = (void *)ee + sizeof(struct bpf_event_entry);
Thanks,
Song
>
>>
>>> -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
>>>
>>
>>
On Fri, 31 May 2019 05:26:30 +0000
Song Liu <[email protected]> wrote:
> We can also do something like
>
> ee = kzalloc(sizeof(struct bpf_event_entry) + sizeof(struct perf_sample_data));
> ee->sd = (void *)ee + sizeof(struct bpf_event_entry);
Or perhaps:
ee->sd = (struct perf_sample_data *)(ee + 1);
-- Steve