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libbpf: Ensure print callback usage is thread-safe

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

Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230325010845.46000-1-inwardvessel@gmail.com
Signed-off-by: Daniel Müller <deso@posteo.net>
This commit is contained in:
JP Kobryn
2023-03-24 18:08:45 -07:00
committed by Andrii Nakryiko
parent b362bb6e10
commit ae32d7169d
2 changed files with 8 additions and 3 deletions
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9
src/libbpf.c
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@@ -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 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; return old_print_fn;
} }
@@ -227,8 +228,10 @@ void libbpf_print(enum libbpf_print_level level, const char *format, ...)
{ {
va_list args; va_list args;
int old_errno; 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; return;
old_errno = errno; old_errno = errno;

2
src/libbpf.h
View File

@@ -101,6 +101,8 @@ typedef int (*libbpf_print_fn_t)(enum libbpf_print_level level,
* be used for libbpf warnings and informational messages. * be used for libbpf warnings and informational messages.
* @param fn The log print function. If NULL, libbpf won't print anything. * @param fn The log print function. If NULL, libbpf won't print anything.
* @return Pointer to old print function. * @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); LIBBPF_API libbpf_print_fn_t libbpf_set_print(libbpf_print_fn_t fn);