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bpf: permit multiple bpf attachments for a single perf event

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This patch enables multiple bpf attachments for a
kprobe/uprobe/tracepoint single trace event.
Each trace_event keeps a list of attached perf events.
When an event happens, all attached bpf programs will
be executed based on the order of attachment.

A global bpf_event_mutex lock is introduced to protect
prog_array attaching and detaching. An alternative will
be introduce a mutex lock in every trace_event_call
structure, but it takes a lot of extra memory.
So a global bpf_event_mutex lock is a good compromise.

The bpf prog detachment involves allocation of memory.
If the allocation fails, a dummy do-nothing program
will replace to-be-detached program in-place.

Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yonghong Song
2017-10-23 23:53:08 -07:00
committed by David S. Miller
parent 0b4c6841fe
commit e87c6bc385
9 changed files with 255 additions and 56 deletions
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43
include/linux/trace_events.h
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@@ -271,14 +271,37 @@ struct trace_event_call {
#ifdef CONFIG_PERF_EVENTS
int perf_refcount;
struct hlist_head __percpu *perf_events;
struct bpf_prog *prog;
struct perf_event *bpf_prog_owner;
struct bpf_prog_array __rcu *prog_array;
int (*perf_perm)(struct trace_event_call *,
struct perf_event *);
#endif
};
#ifdef CONFIG_PERF_EVENTS
static inline bool bpf_prog_array_valid(struct trace_event_call *call)
{
/*
* This inline function checks whether call->prog_array
* is valid or not. The function is called in various places,
* outside rcu_read_lock/unlock, as a heuristic to speed up execution.
*
* If this function returns true, and later call->prog_array
* becomes false inside rcu_read_lock/unlock region,
* we bail out then. If this function return false,
* there is a risk that we might miss a few events if the checking
* were delayed until inside rcu_read_lock/unlock region and
* call->prog_array happened to become non-NULL then.
*
* Here, READ_ONCE() is used instead of rcu_access_pointer().
* rcu_access_pointer() requires the actual definition of
* "struct bpf_prog_array" while READ_ONCE() only needs
* a declaration of the same type.
*/
return !!READ_ONCE(call->prog_array);
}
#endif
static inline const char *
trace_event_name(struct trace_event_call *call)
{
@@ -435,12 +458,23 @@ trace_trigger_soft_disabled(struct trace_event_file *file)
}
#ifdef CONFIG_BPF_EVENTS
unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx);
unsigned int trace_call_bpf(struct trace_event_call *call, void *ctx);
int perf_event_attach_bpf_prog(struct perf_event *event, struct bpf_prog *prog);
void perf_event_detach_bpf_prog(struct perf_event *event);
#else
static inline unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
static inline unsigned int trace_call_bpf(struct trace_event_call *call, void *ctx)
{
return 1;
}
static inline int
perf_event_attach_bpf_prog(struct perf_event *event, struct bpf_prog *prog)
{
return -EOPNOTSUPP;
}
static inline void perf_event_detach_bpf_prog(struct perf_event *event) { }
#endif
enum {
@@ -511,6 +545,7 @@ perf_trace_buf_submit(void *raw_data, int size, int rctx, u16 type,
{
perf_tp_event(type, count, raw_data, size, regs, head, rctx, task, event);
}
#endif
#endif /* _LINUX_TRACE_EVENT_H */