Commit f1cb927c authored by JP Kobryn's avatar JP Kobryn Committed by Andrii Nakryiko
Browse files

libbpf: Ensure print callback usage is thread-safe 



This patch prevents races on the print function pointer, allowing the
libbpf_set_print() function to become thread-safe.

Signed-off-by: default avatarJP Kobryn <inwardvessel@gmail.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230325010845.46000-1-inwardvessel@gmail.com
parent 5f5a7d8d

tools/lib/bpf/libbpf.c

+6 −3
Original line number Diff line number Diff line
@@ -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;

tools/lib/bpf/libbpf.h

+2 −0
Original line number Diff line number Diff line
@@ -101,6 +101,8 @@ typedef int (*libbpf_print_fn_t)(enum libbpf_print_level level, 
 * be used for libbpf warnings and informational messages.

 * @param fn The log print function. If NULL, libbpf won't print anything.

 * @return Pointer to old print function.

 *

 * This function is thread-safe.

 */

LIBBPF_API libbpf_print_fn_t libbpf_set_print(libbpf_print_fn_t fn);