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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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82
kernel/trace/bpf_trace.c
View File

@@ -17,7 +17,7 @@
/**
* trace_call_bpf - invoke BPF program
* @prog: BPF program
* @call: tracepoint event
* @ctx: opaque context pointer
*
* kprobe handlers execute BPF programs via this helper.
@@ -29,7 +29,7 @@
* 1 - store kprobe event into ring buffer
* Other values are reserved and currently alias to 1
*/
unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
unsigned int trace_call_bpf(struct trace_event_call *call, void *ctx)
{
unsigned int ret;
@@ -49,9 +49,22 @@ unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
goto out;
}
rcu_read_lock();
ret = BPF_PROG_RUN(prog, ctx);
rcu_read_unlock();
/*
* Instead of moving rcu_read_lock/rcu_dereference/rcu_read_unlock
* to all call sites, we did a bpf_prog_array_valid() there to check
* whether call->prog_array is empty or not, which is
* a heurisitc to speed up execution.
*
* If bpf_prog_array_valid() fetched prog_array was
* non-NULL, we go into trace_call_bpf() and do the actual
* proper rcu_dereference() under RCU lock.
* If it turns out that prog_array is NULL then, we bail out.
* For the opposite, if the bpf_prog_array_valid() fetched pointer
* was NULL, you'll skip the prog_array with the risk of missing
* out of events when it was updated in between this and the
* rcu_dereference() which is accepted risk.
*/
ret = BPF_PROG_RUN_ARRAY_CHECK(call->prog_array, ctx, BPF_PROG_RUN);
out:
__this_cpu_dec(bpf_prog_active);
@@ -741,3 +754,62 @@ const struct bpf_verifier_ops perf_event_verifier_ops = {
const struct bpf_prog_ops perf_event_prog_ops = {
};
static DEFINE_MUTEX(bpf_event_mutex);
int perf_event_attach_bpf_prog(struct perf_event *event,
struct bpf_prog *prog)
{
struct bpf_prog_array __rcu *old_array;
struct bpf_prog_array *new_array;
int ret = -EEXIST;
mutex_lock(&bpf_event_mutex);
if (event->prog)
goto out;
old_array = rcu_dereference_protected(event->tp_event->prog_array,
lockdep_is_held(&bpf_event_mutex));
ret = bpf_prog_array_copy(old_array, NULL, prog, &new_array);
if (ret < 0)
goto out;
/* set the new array to event->tp_event and set event->prog */
event->prog = prog;
rcu_assign_pointer(event->tp_event->prog_array, new_array);
bpf_prog_array_free(old_array);
out:
mutex_unlock(&bpf_event_mutex);
return ret;
}
void perf_event_detach_bpf_prog(struct perf_event *event)
{
struct bpf_prog_array __rcu *old_array;
struct bpf_prog_array *new_array;
int ret;
mutex_lock(&bpf_event_mutex);
if (!event->prog)
goto out;
old_array = rcu_dereference_protected(event->tp_event->prog_array,
lockdep_is_held(&bpf_event_mutex));
ret = bpf_prog_array_copy(old_array, event->prog, NULL, &new_array);
if (ret < 0) {
bpf_prog_array_delete_safe(old_array, event->prog);
} else {
rcu_assign_pointer(event->tp_event->prog_array, new_array);
bpf_prog_array_free(old_array);
}
bpf_prog_put(event->prog);
event->prog = NULL;
out:
mutex_unlock(&bpf_event_mutex);
}