pidfd: implement PIDFD_THREAD flag for pidfd_open()

[linux-2.6-block.git] / kernel / fork.c

diff --git a/kernel/fork.c b/kernel/fork.c
index 726a92043531ffa27df804192cf266685f18b3ba..1a9b910559169c2bec683948c74475dcd77a5048 100644 (file)
--- 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) {
@@ -2068,22 +2071,35 @@ 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);
-
        /*
-        * Inform pollers only when the whole thread group exits.
-        * If the thread group leader exits before all other threads in the
-        * group, then poll(2) should block, similar to the wait(2) family.
+        * Depending on PIDFD_THREAD, inform pollers when the thread
+        * or the whole thread-group exits.
         */
-       if (thread_group_exited(pid))
+       if (pidfd_task_exited(pid, thread))
                poll_flags = EPOLLIN | EPOLLRDNORM;
 
        return poll_flags;
@@ -2141,6 +2157,11 @@ 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;
 }
@@ -2154,7 +2175,8 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re
  * Allocate a new file that stashes @pid and reserve a new pidfd number in the
  * caller's file descriptor table. The pidfd is reserved but not installed yet.
  *
- * The helper verifies that @pid is used as a thread group leader.
+ * The helper verifies that @pid is still in use, without PIDFD_THREAD the
+ * task identified by @pid must be a thread-group leader.
  *
  * If this function returns successfully the caller is responsible to either
  * call fd_install() passing the returned pidfd and pidfd file as arguments in
@@ -2173,7 +2195,9 @@ 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);