Re: [AIO] aio-2.6.13-rc6-B1

[Benjamin LaHaise <bcrl@linux.intel.com>]

On Tue, Sep 20, 2005 at 12:23:10PM +0200, Sébastien Dugué wrote:
>   what's the point of calling wake_up_locked(&sem->wait) in 
> aio_down_wait? We're already in a wakeup path and end up
> calling __wake_up_common recursively.

That's necessary to kick the next semaphore op in the list.  The 
list_del_init() right above that makes sure that we don't recurse 
and run the routine again.

>   I think it may be one of the cause of my kernel hanging at the
> very beginning.
> 
>   When I remove this call things go further but at some point a
> semaphore wait queue gets thrashed and __wake_up_common tries to
> call an invalid callback function.

This patch from Zach might make a difference.  Let me know if it changes 
the symptoms at all.  Sorry if it doesn't apply cleanly, as it is against 
a base kernel.  Basically, we could sleep while holding ctx_lock, which 
does Bad Things(tm) on SMP systems.

		-ben


Index: 2.6.13-git12-lock-kiocb/fs/aio.c
===================================================================
--- 2.6.13-git12-lock-kiocb.orig/fs/aio.c
+++ 2.6.13-git12-lock-kiocb/fs/aio.c
@@ -398,7 +398,7 @@ static struct kiocb fastcall *__aio_get_
 	if (unlikely(!req))
 		return NULL;
 
-	req->ki_flags = 1 << KIF_LOCKED;
+	req->ki_flags = 0;
 	req->ki_users = 2;
 	req->ki_key = 0;
 	req->ki_ctx = ctx;
@@ -717,6 +717,8 @@ static ssize_t aio_run_iocb(struct kiocb
 	iocb->ki_run_list.next = iocb->ki_run_list.prev = NULL;
 	spin_unlock_irq(&ctx->ctx_lock);
 
+	lock_kiocb(iocb);
+
 	/* Quit retrying if the i/o has been cancelled */
 	if (kiocbIsCancelled(iocb)) {
 		ret = -EINTR;
@@ -781,6 +783,7 @@ out:
 			aio_queue_work(ctx);
 		}
 	}
+	unlock_kiocb(iocb);
 	return ret;
 }
 
@@ -805,9 +808,7 @@ static int __aio_run_iocbs(struct kioctx
 		 * Hold an extra reference while retrying i/o.
 		 */
 		iocb->ki_users++;       /* grab extra reference */
-		lock_kiocb(iocb);
 		aio_run_iocb(iocb);
-		unlock_kiocb(iocb);
 		if (__aio_put_req(ctx, iocb))  /* drop extra ref */
 			put_ioctx(ctx);
  	}
@@ -1549,7 +1550,6 @@ int fastcall io_submit_one(struct kioctx
 
 	spin_lock_irq(&ctx->ctx_lock);
 	aio_run_iocb(req);
-	unlock_kiocb(req);
 	if (!list_empty(&ctx->run_list)) {
 		/* drain the run list */
 		while (__aio_run_iocbs(ctx))