[RFC PATCH] pidfd: implement PIDFD_THREAD flag for pidfd_open()
From: Oleg Nesterov <oleg@redhat.com>
Date: 2024-01-29 11:24:39
Also in:
lkml
Subsystem:
exec & binfmt api, elf, memory management - core, scheduler, the rest · Maintainers:
Kees Cook, Andrew Morton, David Hildenbrand, Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Linus Torvalds
On 01/27, Oleg Nesterov wrote:
I'll (hopefully) send v2 on top of pidfd: cleanup the usage of __pidfd_prepare's flags pidfd: don't do_notify_pidfd() if !thread_group_empty() on Monday
Sorry, I don't have time to finish v2 today, I need to update the comments and write the changelog. But the patch itself is ready, I am sending it for review. Tycho, Christian, any comments? Oleg. From c31780f6c1136a72048d24701ac6d8401fc1afda Mon Sep 17 00:00:00 2001 From: Oleg Nesterov <oleg@redhat.com> Date: Sat, 27 Jan 2024 16:59:18 +0100 Subject: [PATCH] pidfd: implement PIDFD_THREAD flag for pidfd_open() --- include/uapi/linux/pidfd.h | 3 ++- kernel/exit.c | 7 +++++++ kernel/fork.c | 29 +++++++++++++++++++++++++++-- kernel/pid.c | 2 +- kernel/signal.c | 4 +++- 5 files changed, 40 insertions(+), 5 deletions(-)
diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h
index 5406fbc13074..2e6461459877 100644
--- a/include/uapi/linux/pidfd.h
+++ b/include/uapi/linux/pidfd.h@@ -7,6 +7,7 @@ #include <linux/fcntl.h> /* Flags for pidfd_open(). */ -#define PIDFD_NONBLOCK O_NONBLOCK +#define PIDFD_NONBLOCK O_NONBLOCK +#define PIDFD_THREAD O_EXCL #endif /* _UAPI_LINUX_PIDFD_H */
diff --git a/kernel/exit.c b/kernel/exit.c
index dfb963d2f862..74fe6bfb9577 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c@@ -739,6 +739,13 @@ static void exit_notify(struct task_struct *tsk, int group_dead) kill_orphaned_pgrp(tsk->group_leader, NULL); tsk->exit_state = EXIT_ZOMBIE; + /* + * sub-thread or delay_group_leader(), wake up the PIDFD_THREAD + * waiters. + */ + if (!thread_group_empty(tsk)) + do_notify_pidfd(tsk); + if (unlikely(tsk->ptrace)) { int sig = thread_group_leader(tsk) && thread_group_empty(tsk) &&
diff --git a/kernel/fork.c b/kernel/fork.c
index 347641398f9d..977b58c0eac6 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c@@ -101,6 +101,7 @@ #include <linux/user_events.h> #include <linux/iommu.h> #include <linux/rseq.h> +#include <uapi/linux/pidfd.h> #include <asm/pgalloc.h> #include <linux/uaccess.h>
@@ -2050,6 +2051,8 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f) seq_put_decimal_ll(m, "Pid:\t", nr); + /* TODO: report PIDFD_THREAD */ + #ifdef CONFIG_PID_NS seq_put_decimal_ll(m, "\nNSpid:\t", nr); if (nr > 0) {
@@ -2068,12 +2071,27 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f) } #endif +static bool pidfd_task_exited(struct pid *pid, bool thread) +{ + struct task_struct *task; + bool exited; + + rcu_read_lock(); + task = pid_task(pid, PIDTYPE_PID); + exited = !task || + (READ_ONCE(task->exit_state) && (thread || thread_group_empty(task))); + rcu_read_unlock(); + + return exited; +} + /* * Poll support for process exit notification. */ static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts) { struct pid *pid = file->private_data; + bool thread = file->f_flags & PIDFD_THREAD; __poll_t poll_flags = 0; poll_wait(file, &pid->wait_pidfd, pts);
@@ -2083,7 +2101,7 @@ static __poll_t pidfd_poll(struct file *file, struct poll_table_struct *pts) * If the thread group leader exits before all other threads in the * group, then poll(2) should block, similar to the wait(2) family. */ - if (thread_group_exited(pid)) + if (pidfd_task_exited(pid, thread)) poll_flags = EPOLLIN | EPOLLRDNORM; return poll_flags;
@@ -2141,6 +2159,11 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re return PTR_ERR(pidfd_file); } get_pid(pid); /* held by pidfd_file now */ + /* + * anon_inode_getfile() ignores everything outside of the + * O_ACCMODE | O_NONBLOCK mask, set PIDFD_THREAD manually. + */ + pidfd_file->f_flags |= (flags & PIDFD_THREAD); *ret = pidfd_file; return pidfd; }
@@ -2173,7 +2196,9 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re */ int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret) { - if (!pid || !pid_has_task(pid, PIDTYPE_TGID)) + bool thread = flags & PIDFD_THREAD; + + if (!pid || !pid_has_task(pid, thread ? PIDTYPE_PID : PIDTYPE_TGID)); return -EINVAL; return __pidfd_prepare(pid, flags, ret);
diff --git a/kernel/pid.c b/kernel/pid.c
index c7a3e359f8f5..04bdd5ecf183 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c@@ -629,7 +629,7 @@ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags) int fd; struct pid *p; - if (flags & ~PIDFD_NONBLOCK) + if (flags & ~(PIDFD_NONBLOCK | PIDFD_THREAD)) return -EINVAL; if (pid <= 0)
diff --git a/kernel/signal.c b/kernel/signal.c
index 9561a3962ca6..919cd33a0405 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c@@ -2051,7 +2051,8 @@ bool do_notify_parent(struct task_struct *tsk, int sig) WARN_ON_ONCE(!tsk->ptrace && (tsk->group_leader != tsk || !thread_group_empty(tsk))); /* - * tsk is a group leader and has no threads, wake up the pidfd waiters. + * tsk is a group leader and has no threads, wake up the !PIDFD_THREAD + * waiters. */ if (thread_group_empty(tsk)) do_notify_pidfd(tsk);
@@ -3926,6 +3927,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig, prepare_kill_siginfo(sig, &kinfo); } + /* TODO: respect PIDFD_THREAD */ ret = kill_pid_info(sig, &kinfo, pid); err:
--
2.25.1.362.g51ebf55