On Fri, Mar 24, 2023 at 6:09 PM JP Kobryn <inwardvessel@xxxxxxxxx> wrote:
>
> 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@xxxxxxxxx>
> ---
I reworked the patch subject to "libbpf: Ensure print callback usage
is thread-safe", it felt more on point. Also changed to "thread-safe",
which seems to be a proper spelling for this term.
Applied to bpf-next, thanks!
> 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.
> + *
I moved this part to after @return spec, where details about functions
are normally put.
> * @param fn The log print function. If NULL, libbpf won't print anything.
> * @return Pointer to old print function.
> */
> --
> 2.39.2
>
