From d28446fe2d87ea344c14741c39962dcc7aee5c78 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@cse.unsw.edu.au>
Date: Sat, 16 Apr 2005 15:26:41 -0700
Subject: [PATCH] [PATCH] md: close a small race in md thread deregistration
There is a tiny race when de-registering an MD thread, in that the thread
could disappear before it is set a SIGKILL, causing send_sig to have
problems.
This is most easily closed by holding tasklist_lock between enabling the
thread to exit (setting ->run to NULL) and telling it to exit.
(akpm: ick. Needs to use kthread API and stop using signals)
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---
drivers/md/md.c | 20 ++++++++------------
1 file changed, 8 insertions(+), 12 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index aa72c88a024f..44a164965546 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2840,16 +2840,6 @@ mdk_thread_t *md_register_thread(void (*run) (mddev_t *), mddev_t *mddev,
return thread;
}
-static void md_interrupt_thread(mdk_thread_t *thread)
-{
- if (!thread->tsk) {
- MD_BUG();
- return;
- }
- dprintk("interrupting MD-thread pid %d\n", thread->tsk->pid);
- send_sig(SIGKILL, thread->tsk, 1);
-}
-
void md_unregister_thread(mdk_thread_t *thread)
{
struct completion event;
@@ -2857,9 +2847,15 @@ void md_unregister_thread(mdk_thread_t *thread)
init_completion(&event);
thread->event = &event;
+
+ /* As soon as ->run is set to NULL, the task could disappear,
+ * so we need to hold tasklist_lock until we have sent the signal
+ */
+ dprintk("interrupting MD-thread pid %d\n", thread->tsk->pid);
+ read_lock(&tasklist_lock);
thread->run = NULL;
- thread->name = NULL;
- md_interrupt_thread(thread);
+ send_sig(SIGKILL, thread->tsk, 1);
+ read_unlock(&tasklist_lock);
wait_for_completion(&event);
kfree(thread);
}