On Thu, 28 Jun 2012 08:34:23 -0400, Josef Bacik wrote: > On Wed, Jun 27, 2012 at 09:35:08PM -0600, Miao Xie wrote: >> On Tue, 26 Jun 2012 09:42:56 -0400, Josef Bacik wrote: >>> From: Josef Bacik <josef@xxxxxxxxxx> >>> >>> Miao pointed out there's a problem with mixing dio writes and buffered >>> reads. If the read happens between us invalidating the page range and >>> actually locking the extent we can bring in pages into page cache. Then >>> once the write finishes if somebody tries to read again it will just find >>> uptodate pages and we'll read stale data. So we need to lock the extent and >>> check for uptodate bits in the range. If there are uptodate bits we need to >>> unlock and invalidate again. This will keep this race from happening since >>> we will hold the extent locked until we create the ordered extent, and then >>> teh read side always waits for ordered extents. Thanks, >> >> This patch still can not work well. It is because we don't update i_size in time. >> Writer Worker Reader >> lock_extent >> do direct io >> end io >> finish io >> unlock_extent >> lock_extent >> check the pos is beyond EOF or not >> beyond EOF, zero the page and set it uptodate >> unlock_extent >> update i_size >> >> So I think we must update the i_size in time, and I wrote a small patch to do it: >> > > We should probably be updating i_size when we create an extent past EOF in the > write stuff, not during endio, I will work this out and fold it into my patch. > Good catch. It is better that update i_size in endio, I think. because during endio, we are sure that the data is flushed into the disk successfully, and can update i_size at ease. and if the error happens when flushing the data into the disk, we also needn't reset i_size. Thanks Miao -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
