[PATCH] pid: make session_of_pgrp use struct pid instead of pid_t

To properly implement a pid namespace I need to deal exclusively in terms of
struct pid, because pid_t values become ambiguous.

To this end session_of_pgrp is transformed to take and return a struct pid
pointer.  To avoid the need to worry about reference counting I now require my
caller to hold the appropriate locks.  Leaving callers repsonsible for
increasing the reference count if they need access to the result outside of
the locks.

Since session_of_pgrp currently only has one caller and that caller simply
uses only test the result for equality with another process group, the locking
change means I don't actually have to acquire the tasklist_lock at all.

tiocspgrp is also modified to take and release the lock.  The logic there is a
little more complicated but nothing I won't need when I convert pgrp of a tty
to a struct pid pointer.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 9 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 14f17033f563..3ac6a7a6f857 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -185,21 +185,19 @@ repeat:
  * This checks not only the pgrp, but falls back on the pid if no
  * satisfactory pgrp is found. I dunno - gdb doesn't work correctly
  * without this...
+ *
+ * The caller must hold rcu lock or the tasklist lock.
  */
-int session_of_pgrp(int pgrp)
+struct pid *session_of_pgrp(struct pid *pgrp)
 {
 	struct task_struct *p;
-	int sid = 0;
-
-	read_lock(&tasklist_lock);
+	struct pid *sid = NULL;
 
-	p = find_task_by_pid_type(PIDTYPE_PGID, pgrp);
+	p = pid_task(pgrp, PIDTYPE_PGID);
 	if (p == NULL)
-		p = find_task_by_pid(pgrp);
+		p = pid_task(pgrp, PIDTYPE_PID);
 	if (p != NULL)
-		sid = process_session(p);
-
-	read_unlock(&tasklist_lock);
+		sid = task_session(p);
 
 	return sid;
 }