Re: [PATCH] zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF_SIGPENDING

Boqun Feng
2024-06-08T17:00:53Z

On Sat, Jun 08, 2024 at 02:06:16PM +0200, Oleg Nesterov wrote:
> kernel_wait4() doesn't sleep and returns -EINTR if there is no
> eligible child and signal_pending() is true.
>
> That is why zap_pid_ns_processes() clears TIF_SIGPENDING but this is not
> enough, it should also clear TIF_NOTIFY_SIGNAL to make signal_pending()
> return false and avoid a busy-wait loop.
>
> Fixes: 12db8b690010 ("entry: Add support for TIF_NOTIFY_SIGNAL")
> Reported-by: Rachel Menge <rachelmenge@linux.microsoft.com>
> Closes: https://lore.kernel.org/all/1386cd49-36d0-4a5c-85e9-bc42056a5a38@linux.microsoft.com/
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>

Wei, appreciate it if you could share some test result and provide a
Tested-by tag. Thanks!

Regards,
Boqun

> ---
> kernel/pid_namespace.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index dc48fecfa1dc..25f3cf679b35 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -218,6 +218,7 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
> */
> do {
> clear_thread_flag(TIF_SIGPENDING);
> + clear_thread_flag(TIF_NOTIFY_SIGNAL);
> rc = kernel_wait4(-1, NULL, __WALL, NULL);
> } while (rc != -ECHILD);
>
> --
> 2.25.1.362.g51ebf55
>
>