On Sat, Feb 10, 2024 at 02:15:18PM +0100, Oleg Nesterov wrote: > On 02/10, Christian Brauner wrote: > > > > The question is what is more useful for userspace when they do: > > pidfd_send_signal(1234, PIDFD_SEND_PROCESS_GROUP)? > > > > (1) They either mean to signal a process group that is headed by 1234. > > Yes, this is what I had in mind, see also another email from me. > Simple, clear, and matches kill(-1234). I went for a walk and kept thinking about this and I agree with you. It will require that 1234 will be a process group leader but I think that this is ok to require that. The implementation becomes a lot simpler of course. >From 6a9d6a6bd8b77cba210b9c28f0e6e047c7956e9f Mon Sep 17 00:00:00 2001 From: Christian Brauner <brauner@xxxxxxxxxx> Date: Fri, 9 Feb 2024 15:49:45 +0100 Subject: [PATCH v2] [RFC] pidfd: allow to override signal scope in pidfd_send_signal() Right now we determine the scope of the signal based on the type of pidfd. There are use-cases where it's useful to override the scope of the signal. For example in [1]. Add flags to determine the scope of the signal: (1) PIDFD_SIGNAL_THREAD: send signal to specific thread referenced by @pidfd (2) PIDFD_SIGNAL_THREAD_GROUP: send signal to thread-group headed by @pidfd (2) PIDFD_SIGNAL_PROCESS_GROUP: send signal to process-group headed by @pidfd Link: https://github.com/systemd/systemd/issues/31093 [1] Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx> --- include/uapi/linux/pidfd.h | 5 +++++ kernel/signal.c | 44 +++++++++++++++++++++++++++++++------- 2 files changed, 41 insertions(+), 8 deletions(-) diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h index 2e6461459877..72ec000a97cd 100644 --- a/include/uapi/linux/pidfd.h +++ b/include/uapi/linux/pidfd.h @@ -10,4 +10,9 @@ #define PIDFD_NONBLOCK O_NONBLOCK #define PIDFD_THREAD O_EXCL +/* Flags for pidfd_send_signal(). */ +#define PIDFD_SIGNAL_THREAD (1UL << 0) +#define PIDFD_SIGNAL_THREAD_GROUP (1UL << 1) +#define PIDFD_SIGNAL_PROCESS_GROUP (1UL << 2) + #endif /* _UAPI_LINUX_PIDFD_H */ diff --git a/kernel/signal.c b/kernel/signal.c index 8b8169623850..cee7cd27ec88 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1905,16 +1905,19 @@ int send_sig_fault_trapno(int sig, int code, void __user *addr, int trapno, return send_sig_info(info.si_signo, &info, t); } -int kill_pgrp(struct pid *pid, int sig, int priv) +static int kill_pgrp_info(int sig, struct kernel_siginfo *info, struct pid *pgrp) { int ret; - read_lock(&tasklist_lock); - ret = __kill_pgrp_info(sig, __si_special(priv), pid); + ret = __kill_pgrp_info(sig, info, pgrp); read_unlock(&tasklist_lock); - return ret; } + +int kill_pgrp(struct pid *pid, int sig, int priv) +{ + return kill_pgrp_info(sig, __si_special(priv), pid); +} EXPORT_SYMBOL(kill_pgrp); int kill_pid(struct pid *pid, int sig, int priv) @@ -3873,6 +3876,10 @@ static struct pid *pidfd_to_pid(const struct file *file) return tgid_pidfd_to_pid(file); } +#define PIDFD_SEND_SIGNAL_FLAGS \ + (PIDFD_SIGNAL_THREAD | PIDFD_SIGNAL_THREAD_GROUP | \ + PIDFD_SIGNAL_PROCESS_GROUP) + /** * sys_pidfd_send_signal - Signal a process through a pidfd * @pidfd: file descriptor of the process @@ -3897,7 +3904,11 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, enum pid_type type; /* Enforce flags be set to 0 until we add an extension. */ - if (flags) + if (flags & ~PIDFD_SEND_SIGNAL_FLAGS) + return -EINVAL; + + /* Ensure that only a single signal scope determining flag is set. */ + if (hweight32(flags & PIDFD_SEND_SIGNAL_FLAGS) > 1) return -EINVAL; f = fdget(pidfd); @@ -3915,10 +3926,24 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, if (!access_pidfd_pidns(pid)) goto err; - if (f.file->f_flags & PIDFD_THREAD) + switch (flags) { + case 0: + /* Infer scope from the type of pidfd. */ + if (f.file->f_flags & PIDFD_THREAD) + type = PIDTYPE_PID; + else + type = PIDTYPE_TGID; + break; + case PIDFD_SIGNAL_THREAD: type = PIDTYPE_PID; - else + break; + case PIDFD_SIGNAL_THREAD_GROUP: type = PIDTYPE_TGID; + break; + case PIDFD_SIGNAL_PROCESS_GROUP: + type = PIDTYPE_PGID; + break; + } if (info) { ret = copy_siginfo_from_user_any(&kinfo, info); @@ -3938,7 +3963,10 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, prepare_kill_siginfo(sig, &kinfo, type); } - ret = kill_pid_info_type(sig, &kinfo, pid, type); + if (type == PIDFD_SIGNAL_PROCESS_GROUP) + ret = kill_pgrp_info(sig, &kinfo, pid); + else + ret = kill_pid_info_type(sig, &kinfo, pid, type); err: fdput(f); return ret; -- 2.43.0
