On 04.10.21 14:50, Christian Brauner wrote:
The number of system calls making use of pidfds is constantly
increasing. Some of those new system calls duplicate the code to turn a
pidfd into task_struct it refers to. Give them a simple helper for this.
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Matthew Bobrowski <repnop@xxxxxxxxxx>
Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
---
include/linux/pid.h | 1 +
kernel/pid.c | 34 ++++++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)
diff --git a/include/linux/pid.h b/include/linux/pid.h
index af308e15f174..343abf22092e 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -78,6 +78,7 @@ struct file;
extern struct pid *pidfd_pid(const struct file *file);
struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
+struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
int pidfd_create(struct pid *pid, unsigned int flags);
static inline struct pid *get_pid(struct pid *pid)
diff --git a/kernel/pid.c b/kernel/pid.c
index efe87db44683..2ffbb87b2ce8 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -539,6 +539,40 @@ struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags)
return pid;
}
+/**
+ * pidfd_get_task() - Get the task associated with a pidfd
+ *
+ * @pidfd: pidfd for which to get the task
+ * @flags: flags associated with this pidfd
+ *
+ * Return the task associated with the given pidfd.
+ * Currently, the process identified by @pidfd is always a thread-group leader.
+ * This restriction currently exists for all aspects of pidfds including pidfd
+ * creation (CLONE_PIDFD cannot be used with CLONE_THREAD) and pidfd polling
+ * (only supports thread group leaders).
+ *
+ * Return: On success, the task_struct associated with the pidfd.
+ * On error, a negative errno number will be returned.
Nice doc.
You might want to document what callers of this function are expected to
do to clean up.
+ */
+struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags)
+{
+ unsigned int f_flags;
+ struct pid *pid;
+ struct task_struct *task;
+
+ pid = pidfd_get_pid(pidfd, &f_flags);
+ if (IS_ERR(pid))
+ return ERR_CAST(pid);
+
+ task = get_pid_task(pid, PIDTYPE_TGID);
+ put_pid(pid);
The code to be replaced always does the put_pid() after the
put_task_struct(). Is this new ordering safe? (didn't check)
+ if (!task)
+ return ERR_PTR(-ESRCH);
+
+ *flags = f_flags;
+ return task;
+}
+
/**
* pidfd_create() - Create a new pid file descriptor.
*
I'd have squashed this into the second patch, makes it a lot easier to
review and it's only a MM cleanup at this point.
--
Thanks,
David / dhildenb
