[PATCH] fix de_thread() vs do_coredump() deadlock

[Oleg Nesterov <oleg@tv-sign.ru>]

de_thread() sends SIGKILL to all sub-threads and
waits them to die in 'D' state. It is possible that
one of the threads already dequeued coredump signal.
When de_thread() unlocks ->sighand->lock that thread
can enter do_coredump()->coredump_wait() and cause a
deadlock.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 2.6.14-rc4/fs/exec.c~	2005-09-21 21:08:33.000000000 +0400
+++ 2.6.14-rc4/fs/exec.c	2005-10-14 00:19:19.000000000 +0400
@@ -1468,11 +1468,21 @@ int do_coredump(long signr, int exit_cod
 		current->fsuid = 0;	/* Dump root private */
 	}
 	mm->dumpable = 0;
-	init_completion(&mm->core_done);
+
+	retval = -EAGAIN;
 	spin_lock_irq(&current->sighand->siglock);
-	current->signal->flags = SIGNAL_GROUP_EXIT;
-	current->signal->group_exit_code = exit_code;
+	if (!(current->signal->flags & SIGNAL_GROUP_EXIT)) {
+		current->signal->flags = SIGNAL_GROUP_EXIT;
+		current->signal->group_exit_code = exit_code;
+		retval = 0;
+	}
 	spin_unlock_irq(&current->sighand->siglock);
+	if (retval) {
+		up_write(&mm->mmap_sem);
+		goto fail;
+	}
+
+	init_completion(&mm->core_done);
 	coredump_wait(mm);
 
 	/*