On Wed, Sep 03, 2014 at 07:21:16PM +1000, Dave Chinner wrote:

quoted

@@ -481,9 +484,14 @@ int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
 		err = dax_get_addr(&bh, &addr, inode->i_blkbits);
 		if (err < 0)
 			return err;
+		/*
+		 * ext4 sometimes asks to zero past the end of a block.  It
+		 * really just wants to zero to the end of the block.
+		 */
+		length = min_t(unsigned, length, PAGE_CACHE_SIZE - offset);
 		memset(addr + offset, 0, length);

Sorry, what?

You introduce that bug with the way dax_truncate_page() is redefined
to always pass PAGE_CACHE_SIZE a a length later on in this patch.
into the function. That's hardly an ext4 bug....

ext4 does (or did?) have this bug (expectation?).  I then take advantage
of the fact that we have to accommodate it, so there are now two places
that have to accommodate it.  I forget what the path was that has that
assumption, but xfstests used to display it.

I'm away this week (... bad timing), but I can certainly fix it elsewhere
in ext4 next week.

quoted

 int dax_clear_blocks(struct inode *, sector_t block, long size);
+int dax_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);
 int dax_truncate_page(struct inode *, loff_t from, get_block_t);

It's still defined as a function that doesn't exist now....

Oops.

quoted

+/* Can't be a function because PAGE_CACHE_SIZE is defined in pagemap.h */
+#define dax_truncate_page(inode, from, get_block)	\
+	dax_zero_page_range(inode, from, PAGE_CACHE_SIZE, get_block)

And then redefined as a macro here.

Heh, which means we never notice the stale delaration above.  Thanks, C!

This is wrong, IMO,
dax_truncate_page() should remain as a function and it should
correctly calculate how much of the page shoul dbe trimmed, not
leave landmines that other code has to clean up...

(Yup, I'm tracking down a truncate bug in XFS from fsx...)

I'll put an assert in the rewrite, make sure that nobody's trying to
overtruncate.

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