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[PATCH] md: close a small race in md thread deregistration

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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>
This commit is contained in:
NeilBrown 2005-04-16 15:26:41 -07:00 committed by Linus Torvalds
parent 187a27845a
commit d28446fe2d
1 changed files with 8 additions and 12 deletions
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20
drivers/md/md.c
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@ -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);
}