[PATCH] exec: allow init to exec from any thread.

After looking at the problem of init calling exec some more I figured out
an easy way to make the code work.

The actual symptom without out this patch is that all threads will die
except pid == 1, and the thread calling exec.  The thread calling exec will
wait forever for pid == 1 to die.

Since pid == 1 does not install a handler for SIGKILL it will never die.

This modifies the tests for init from current->pid == 1 to the equivalent
current == child_reaper.  And then it causes exec in the ugly case to
modify child_reaper.

The only weird symptom is that you wind up with an init process that
doesn't have the oldest start time on the box.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 14 insertions, 3 deletions

diff --git a/fs/exec.c b/fs/exec.c
index c7397c46ad6d..d0ecea0781f7 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -660,12 +660,23 @@ static int de_thread(struct task_struct *tsk)
                 struct dentry *proc_dentry1, *proc_dentry2;
                 unsigned long ptrace;
 
+                leader = current->group_leader;
+                /*
+                 * If our leader is the child_reaper become
+                 * the child_reaper and resend SIGKILL signal.
+                 */
+                if (unlikely(leader == child_reaper)) {
+                        write_lock(&tasklist_lock);
+                        child_reaper = current;
+                        zap_other_threads(current);
+                        write_unlock(&tasklist_lock);
+                }
+
                 /*
                  * Wait for the thread group leader to be a zombie.
                  * It should already be zombie at this point, most
                  * of the time.
                  */
-                leader = current->group_leader;
                 while (leader->exit_state != EXIT_ZOMBIE)
                         yield();
 
diff --git a/kernel/exit.c b/kernel/exit.c
index a8c7efc7a681..223a8802b665 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -807,7 +807,7 @@ fastcall NORET_TYPE void do_exit(long code)
                 panic("Aiee, killing interrupt handler!");
         if (unlikely(!tsk->pid))
                 panic("Attempted to kill the idle task!");
-        if (unlikely(tsk->pid == 1))
+        if (unlikely(tsk == child_reaper))
                 panic("Attempted to kill init!");
 
         if (unlikely(current->ptrace & PT_TRACE_EXIT)) {
diff --git a/kernel/signal.c b/kernel/signal.c
index 75f7341b0c39..dc8f91bf9f89 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1990,7 +1990,7 @@ relock:
                         continue;
 
                 /* Init gets no signals it doesn't want.  */
-                if (current->pid == 1)
+                if (current == child_reaper)
                         continue;
 
                 if (sig_kernel_stop(signr)) {