bpf: Use dedicated bpf_trace_printk event instead of trace_printk()
The bpf helper bpf_trace_printk() uses trace_printk() under the hood.
This leads to an alarming warning message originating from trace
buffer allocation which occurs the first time a program using
bpf_trace_printk() is loaded.
We can instead create a trace event for bpf_trace_printk() and enable
it in-kernel when/if we encounter a program using the
bpf_trace_printk() helper. With this approach, trace_printk()
is not used directly and no warning message appears.
This work was started by Steven (see Link) and finished by Alan; added
Steven's Signed-off-by with his permission.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/r/20200628194334.6238b933@oasis.local.home
Link: https://lore.kernel.org/bpf/1594641154-18897-2-git-send-email-alan.maguire@oracle.com
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index e178e8e..3cc0dcb 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -11,6 +11,7 @@
#include <linux/uaccess.h>
#include <linux/ctype.h>
#include <linux/kprobes.h>
+#include <linux/spinlock.h>
#include <linux/syscalls.h>
#include <linux/error-injection.h>
#include <linux/btf_ids.h>
@@ -20,6 +21,9 @@
#include "trace_probe.h"
#include "trace.h"
+#define CREATE_TRACE_POINTS
+#include "bpf_trace.h"
+
#define bpf_event_rcu_dereference(p) \
rcu_dereference_protected(p, lockdep_is_held(&bpf_event_mutex))
@@ -375,6 +379,30 @@ static void bpf_trace_copy_string(char *buf, void *unsafe_ptr, char fmt_ptype,
}
}
+static DEFINE_RAW_SPINLOCK(trace_printk_lock);
+
+#define BPF_TRACE_PRINTK_SIZE 1024
+
+static inline __printf(1, 0) int bpf_do_trace_printk(const char *fmt, ...)
+{
+ static char buf[BPF_TRACE_PRINTK_SIZE];
+ unsigned long flags;
+ va_list ap;
+ int ret;
+
+ raw_spin_lock_irqsave(&trace_printk_lock, flags);
+ va_start(ap, fmt);
+ ret = vsnprintf(buf, sizeof(buf), fmt, ap);
+ va_end(ap);
+ /* vsnprintf() will not append null for zero-length strings */
+ if (ret == 0)
+ buf[0] = '\0';
+ trace_bpf_trace_printk(buf);
+ raw_spin_unlock_irqrestore(&trace_printk_lock, flags);
+
+ return ret;
+}
+
/*
* Only limited trace_printk() conversion specifiers allowed:
* %d %i %u %x %ld %li %lu %lx %lld %lli %llu %llx %p %pB %pks %pus %s
@@ -484,8 +512,7 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
*/
#define __BPF_TP_EMIT() __BPF_ARG3_TP()
#define __BPF_TP(...) \
- __trace_printk(0 /* Fake ip */, \
- fmt, ##__VA_ARGS__)
+ bpf_do_trace_printk(fmt, ##__VA_ARGS__)
#define __BPF_ARG1_TP(...) \
((mod[0] == 2 || (mod[0] == 1 && __BITS_PER_LONG == 64)) \
@@ -522,10 +549,15 @@ static const struct bpf_func_proto bpf_trace_printk_proto = {
const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
{
/*
- * this program might be calling bpf_trace_printk,
- * so allocate per-cpu printk buffers
+ * This program might be calling bpf_trace_printk,
+ * so enable the associated bpf_trace/bpf_trace_printk event.
+ * Repeat this each time as it is possible a user has
+ * disabled bpf_trace_printk events. By loading a program
+ * calling bpf_trace_printk() however the user has expressed
+ * the intent to see such events.
*/
- trace_printk_init_buffers();
+ if (trace_set_clr_event("bpf_trace", "bpf_trace_printk", 1))
+ pr_warn_ratelimited("could not enable bpf_trace_printk events");
return &bpf_trace_printk_proto;
}