On Wed, Dec 18, 2013 at 09:12:41PM -0700, Matthew Wilcox wrote: > Now that I've spent the best part of a day looking at the ext4 code, I > still don't think there's a problem here. With the way the XIP code is > currently written (calling ext4_get_block with create=1), we won't get an > uninitialised extent in the caller. Instead, we'll get one that's been > zeroed (the zeroing is part of patch 3/3 and done only for xip files). If the block was originally allocated via fallocate(2), it will be marked as uninitialized. When you call ext4_get_block(), if the block has been allocated, it will be returned --- and ext4_map_block() as called by ext4_get_block() does ****not*** clear the uninitialized flag. It can't do so because it would be racy; you can only clear the flag once the data blocks has been written. As far as patch 3/3, it clears the pages in the page cache, but it doesn't zap them in the XIP storage device. But it only does this on the code path when it allocated a block. But if the block has already been previously mapped via fallocate(2), you never hit this section of code. Regards, - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
