linux-kernel - Re: [Linux-NTFS-Dev] 2.6.23 regression: second access of empty ntfs file leads to D state hang

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Date:	Tue, 30 Oct 2007 09:00:02 +0100
From:	Mike Galbraith <efault@....de>
To:	Anton Altaparmakov <aia21@....ac.uk>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	linux-ntfs-dev@...ts.sourceforge.net, Neil Brown <neilb@...e.de>
Subject: Re: [Linux-NTFS-Dev] 2.6.23 regression: second access of empty
	ntfs file leads to D	state hang

On Mon, 2007-10-29 at 16:18 +0100, Mike Galbraith wrote:
> On Mon, 2007-10-29 at 15:43 +0100, Mike Galbraith wrote:
> > On Mon, 2007-10-29 at 13:39 +0000, Anton Altaparmakov wrote:
> > > Hi Mike,
> > > 
> > > Thanks for the files.  That is really odd.  And you are sure this just  
> > > works with 2.6.22.10 on the exact same file?  Have you run  "chkdsk / 
> > > f /v /x" on the NTFS volume from Windows?
> > 
> > Yes, 2.6.22.10 can md5sum that file just fine, did it several times.  I
> > haven't run chkdsk.
> 
> I now have fun chkdsk, it didn't gripe, and the error is still present.

Not being very good at walking away from unsolved mysteries, I chased it
down.  The problem is that...
	commit[a32ea1e1f925399e0d81ca3f7394a44a6dafa12c] Fix read/truncate race
...calls ntfs_readpage() for a zero i_size inode, which it isn't
accustomed to.

Below is the hammer which made my box a happy camper again.

diff --git a/fs/ntfs/aops.c b/fs/ntfs/aops.c
index 6e5c253..ddab5a3 100644
--- a/fs/ntfs/aops.c
+++ b/fs/ntfs/aops.c
@@ -401,7 +401,7 @@ static int ntfs_readpage(struct file *file, struct page *page)
 	MFT_RECORD *mrec;
 	unsigned long flags;
 	u32 attr_len;
-	int err = 0;
+	int err = 0, once = 0;
 
 retry_readpage:
 	BUG_ON(!PageLocked(page));
@@ -414,6 +414,18 @@ retry_readpage:
 		return 0;
 	}
 	vi = page->mapping->host;
+	/*
+	 * If we've been called to read a zero sized inode, zero and bail.
+	 */
+	if (!once) {
+		loff_t i_size = i_size_read(vi);
+
+		once++;
+		if (!i_size) {
+			zero_user_page(page, 0, PAGE_CACHE_SIZE, KM_USER0);
+			goto done;
+		}
+	}
 	ni = NTFS_I(vi);
 	/*
 	 * Only $DATA attributes can be encrypted and only unnamed $DATA


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