linux-kernel - Re: [PATCH] add check do_direct

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Date:	Thu, 26 Jul 2007 22:13:07 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joe Jin <joe.jin@...cle.com>
Cc:	torvalds@...ux-foundation.org, jens.axboe@...cle.com,
	linux-kernel@...r.kernel.org, gurudas.pai@...cle.com,
	wen.gang.wang@...cle.com, Badari Pulavarty <pbadari@...ibm.com>,
	Zach Brown <zach.brown@...cle.com>
Subject: Re: [PATCH] add check do_direct_IO() return val

On Thu, 26 Jul 2007 17:04:00 +0800 Joe Jin <joe.jin@...cle.com> wrote:

> This is the patch for check do_direct_IO() return val.
> 
> At do_direct_IO(), sometimes dio_get_page() will return -EFAULT/-ENOMEM,
> according to orig source, it will go on left work. buf for dio_get_page()
> return a error will made many useful member of dio not initialized like
> dio->map_bh and others, at this point, kernel will panic.
> 
> Signed-off-by: Joe Jin <joe.jin@...cle.com>
> 
> 
> ---
> --- linux-2.6.22/fs/direct-io.c.orig	2007-07-26 11:32:27.000000000 +0800
> +++ linux-2.6.22/fs/direct-io.c	2007-07-26 11:33:58.000000000 +0800
> @@ -1031,7 +1031,9 @@ direct_io_worker(int rw, struct kiocb *i
>  			((dio->final_block_in_request - dio->block_in_file) <<
>  					blkbits);
>  
> -		if (ret) {
> +		if (ret == -EFAULT || ret == -ENOMEM) 
> +			goto out;
> +		else if (ret) {
>  			dio_cleanup(dio);
>  			break;
>  		}
> @@ -1113,6 +1115,7 @@ direct_io_worker(int rw, struct kiocb *i
>  	} else
>  		BUG_ON(ret != -EIOCBQUEUED);
>  
> +out:
>  	return ret;
>  }
>  

I think we still want to run dio_cleanup() if do_direct_IO() failed? 
Otherwise we can leak pages.

And there's nothing special about EFAULT or ENOMEM here: if do_direct_IO()
returns any error then that's it: we bale out, yes?

In fact I'm suspecting that this is what the code in there used to do. 
Something like:

	for (...) {
		...
		ret = do_direct_IO(...);
		...
		if (ret) {
			dio_dleanup(dio);
			break
		}
	}
	return ret;

but then someone later came along and added more code between the end of
the for loop and the `return' statement.

<I do miss the BK diffviewer sometimes>

<does a binary search>

yep, that's exactly what happened.  We broke it in the 2.5.45 release back
in October 2002. (Where "we" == "Badari")

So I think what we need to do is something close to this:

--- a/fs/direct-io.c~add-check-do_direct_io-return-val
+++ a/fs/direct-io.c
@@ -1033,7 +1033,7 @@ direct_io_worker(int rw, struct kiocb *i
 
 		if (ret) {
 			dio_cleanup(dio);
-			break;
+			goto out;
 		}
 	} /* end iovec loop */
 
@@ -1112,7 +1112,7 @@ direct_io_worker(int rw, struct kiocb *i
 		kfree(dio);
 	} else
 		BUG_ON(ret != -EIOCBQUEUED);
-
+out:
 	return ret;
 }
 
_

However I'd like to ask you guys to carefully review and test that please.

-
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