From: Sukadev Bhattiprolu <[EMAIL PROTECTED]>
Subject: [RFC][PATCH 09/14] Save leaders struct pid before detach_pid()
Save the struct pid of the thread group leader before detaching
our pid. See comments in the code below for more details.
Signed-off-by: Sukadev Bhattiprolu <[EMAIL PROTECTED]>
---
fs/exec.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
Index: lx26-21-rc3-mm2/fs/exec.c
===================================================================
--- lx26-21-rc3-mm2.orig/fs/exec.c 2007-03-20 15:55:52.000000000 -0700
+++ lx26-21-rc3-mm2/fs/exec.c 2007-03-20 17:17:38.000000000 -0700
@@ -578,6 +578,7 @@ static int de_thread(struct task_struct
struct sighand_struct *newsighand, *oldsighand = tsk->sighand;
spinlock_t *lock = &oldsighand->siglock;
struct task_struct *leader = NULL;
+ struct pid *leader_pid;
int count;
/*
@@ -698,10 +699,24 @@ static int de_thread(struct task_struct
* The old leader becomes a thread of the this thread group.
* Note: The old leader also uses this pid until release_task
* is called. Odd but simple and correct.
+ * Note: Support for multiple pid namespaces implies that there
+ * can be multiple processes with a given pid_t value,
+ * and so, find_pid() needs/uses a notion of "current"
+ * pid namespace to select the appropriate process to
+ * return.
+ *
+ * Since the current pid namespace of a process is stored
+ * in its pid->pid_nrs list, if we detach/free our struct
+ * pid, we would have no way of finding our current pid
+ * namespace and so no way of finding the leader pid.
+ *
+ * To work around, find the leader pid, before detaching
+ * our pid from the task.
*/
+ leader_pid = find_pid(leader->pid);
detach_pid(tsk, PIDTYPE_PID);
tsk->pid = leader->pid;
- attach_pid(tsk, PIDTYPE_PID, find_pid(tsk->pid));
+ attach_pid(tsk, PIDTYPE_PID, leader_pid);
transfer_pid(leader, tsk, PIDTYPE_PGID);
transfer_pid(leader, tsk, PIDTYPE_SID);
list_replace_rcu(&leader->tasks, &tsk->tasks);
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