Commit 8b401f9ed244 ("bpf: implement bpf_send_signal() helper") added helper bpf_send_signal() which permits bpf program to send a signal to the current process. The signal may be delivered to any threads in the process. We found a use case where sending the signal to the current thread is more preferable. - A bpf program will collect the stack trace and then send signal to the user application. - The user application will add some thread specific information to the just collected stack trace for later analysis. If bpf_send_signal() is used, user application will need to check whether the thread receiving the signal matches the thread collecting the stack by checking thread id. If not, it will need to send signal to another thread through pthread_kill(). This patch proposed a new helper bpf_send_signal_thread(), which sends the signal to the thread corresponding to the current kernel task. This way, user space is guaranteed that bpf_program execution context and user space signal handling context are the same thread.
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| @@ -2714,7 +2714,8 @@ union bpf_attr { · 2713 unmodified lines | ||
| 2714 | 2714 | * |
| 2715 | 2715 | * int bpf_send_signal(u32 sig) |
| 2716 | 2716 | * Description |
| 2717 | − * Send signal *sig* to the current task. | |
| 2717 | + * Send signal *sig* to the process of the current task. | |
| 2718 | + * The signal may be delivered to any of this process's threads. | |
| 2718 | 2719 | * Return |
| 2719 | 2720 | * 0 on success or successfully queued. |
| 2720 | 2721 | * |
| @@ -2850,6 +2851,19 @@ union bpf_attr { · 129 unmodified lines | ||
| 2850 | 2851 | * Return |
| 2851 | 2852 | * 0 on success, or a negative error in case of failure. |
| 2852 | 2853 | * |
| 2854 | + * int bpf_send_signal_thread(u32 sig) | |
| 2855 | + * Description | |
| 2856 | + * Send signal *sig* to the thread corresponding to the current task. | |
| 2857 | + * Return | |
| 2858 | + * 0 on success or successfully queued. | |
| 2859 | + * | |
| 2860 | + * **-EBUSY** if work queue under nmi is full. | |
| 2861 | + * | |
| 2862 | + * **-EINVAL** if *sig* is invalid. | |
| 2863 | + * | |
| 2864 | + * **-EPERM** if no permission to send the *sig*. | |
| 2865 | + * | |
| 2866 | + * **-EAGAIN** if bpf program can try again. | |
| 2853 | 2867 | */ |
| 2854 | 2868 | #define __BPF_FUNC_MAPPER(FN) \ |
| 2855 | 2869 | FN(unspec), \ |
| @@ -2968,7 +2982,8 @@ union bpf_attr { · 112 unmodified lines | ||
| 2968 | 2982 | FN(probe_read_kernel), \ |
| 2969 | 2983 | FN(probe_read_user_str), \ |
| 2970 | 2984 | FN(probe_read_kernel_str), \ |
| 2971 | − FN(tcp_send_ack), | |
| 2985 | + FN(tcp_send_ack), \ | |
| 2986 | + FN(send_signal_thread), | |
| 2972 | 2987 | |
| 2973 | 2988 | /* integer value in 'imm' field of BPF_CALL instruction selects which helper |
| 2974 | 2989 | * function eBPF program intends to call |