On 03/24, JP Kobryn wrote:
This patch prevents races on the print function pointer, allowing the
libbpf_set_print() function to become thread safe.
Why does it have to be thread-safe? The rest of the APIs aren't, so
why can't use solve it on your side by wrapping those calls with a
mutex?
(is there some context I'm missing?)
Signed-off-by: JP Kobryn <inwardvessel@xxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 9 ++++++---
tools/lib/bpf/libbpf.h | 3 +++
2 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index f6a071db5c6e..15737d7b5a28 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -216,9 +216,10 @@ static libbpf_print_fn_t __libbpf_pr = __base_pr;
libbpf_print_fn_t libbpf_set_print(libbpf_print_fn_t fn)
{
- libbpf_print_fn_t old_print_fn = __libbpf_pr;
+ libbpf_print_fn_t old_print_fn;
+
+ old_print_fn = __atomic_exchange_n(&__libbpf_pr, fn, __ATOMIC_RELAXED);
- __libbpf_pr = fn;
return old_print_fn;
}
@@ -227,8 +228,10 @@ void libbpf_print(enum libbpf_print_level level,
const char *format, ...)
{
va_list args;
int old_errno;
+ libbpf_print_fn_t print_fn;
- if (!__libbpf_pr)
+ print_fn = __atomic_load_n(&__libbpf_pr, __ATOMIC_RELAXED);
+ if (!print_fn)
return;
old_errno = errno;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 1615e55e2e79..4478809ff9ca 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -99,6 +99,9 @@ typedef int (*libbpf_print_fn_t)(enum
libbpf_print_level level,
/**
* @brief **libbpf_set_print()** sets user-provided log callback
function to
* be used for libbpf warnings and informational messages.
+ *
+ * This function is thread safe.
+ *
* @param fn The log print function. If NULL, libbpf won't print
anything.
* @return Pointer to old print function.
*/
--
2.39.2
