[PATCH] don't do exit_io_context() until we know we won't be doing any IO

testcase:

mount /dev/sdb10 /mnt
touch /mnt/tmp/b
umount /mnt
mount /dev/sdb10 /mnt
rm /mnt/tmp/b </mnt/tmp/b
umount /mnt

and watch blkdev_ioc line in /proc/slabinfo.  Vanilla kernel leaks.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/exit.c

@@ -807,8 +807,6 @@ fastcall NORET_TYPE void do_exit(long code)
 		panic("Attempted to kill the idle task!");
 	if (unlikely(tsk->pid == 1))
 		panic("Attempted to kill init!");
-	if (tsk->io_context)
-		exit_io_context();
 
 	if (unlikely(current->ptrace & PT_TRACE_EXIT)) {
 		current->ptrace_message = code;
@@ -822,6 +820,8 @@ fastcall NORET_TYPE void do_exit(long code)
 	if (unlikely(tsk->flags & PF_EXITING)) {
 		printk(KERN_ALERT
 			"Fixing recursive fault but reboot is needed!\n");
+		if (tsk->io_context)
+			exit_io_context();
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		schedule();
 	}
@@ -881,6 +881,9 @@ fastcall NORET_TYPE void do_exit(long code)
 	 */
 	mutex_debug_check_no_locks_held(tsk);
 
+	if (tsk->io_context)
+		exit_io_context();
+
 	/* PF_DEAD causes final put_task_struct after we schedule. */
 	preempt_disable();
 	BUG_ON(tsk->flags & PF_DEAD);