"Serge E. Hallyn" <[email protected]> wrote:
>
> Convert loop.c from the deprecated kernel_thread to kthread.
>
I think you have a racelet here:
> + }
> spin_unlock_irq(&lo->lo_lock);
>
> - BUG_ON(!bio);
> - loop_handle_bio(lo, bio);
> -
> - /*
> - * upped both for pending work and tear-down, lo_pending
> - * will hit zero then
> - */
> - if (unlikely(!pending))
> - break;
> + __set_current_state(TASK_INTERRUPTIBLE);
> + schedule();
> }
>
> - complete(&lo->lo_done);
> return 0;
> }
: if (kthread_should_stop()) {
: spin_unlock_irq(&lo->lo_lock);
: break;
: }
: spin_unlock_irq(&lo->lo_lock);
:
: __set_current_state(TASK_INTERRUPTIBLE);
: schedule();
:
If the wake_up_process() is delivered before the __set_current_state(),
we'll miss the wakeup.
If so, this should plug it. The same race is not possible against the
loop_set_fd() wakeup because the thread isn't running at that stage, yes?
diff -puN drivers/block/loop.c~kthread-convert-loopc-to-kthread-race-fix drivers/block/loop.c
--- a/drivers/block/loop.c~kthread-convert-loopc-to-kthread-race-fix
+++ a/drivers/block/loop.c
@@ -525,8 +525,8 @@ static int loop_make_request(request_que
goto out;
lo->lo_pending++;
loop_add_bio(lo, old_bio);
- spin_unlock_irq(&lo->lo_lock);
wake_up_process(lo->lo_thread);
+ spin_unlock_irq(&lo->lo_lock);
return 0;
out:
@@ -600,9 +600,8 @@ static int loop_thread(void *data)
spin_unlock_irq(&lo->lo_lock);
break;
}
- spin_unlock_irq(&lo->lo_lock);
-
__set_current_state(TASK_INTERRUPTIBLE);
+ spin_unlock_irq(&lo->lo_lock);
schedule();
}
_
-
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