Is there something wrong with my question? I asked it 1.5 months ago... Meanwhile, we're using this patch on our database server since Aug-2011, and it appears to work correctly - direct and buffered I/O works together without surprizes. Without this patch, I see unexpected results. Thanks, /mjt On 01.12.2011 00:38, Michael Tokarev wrote: > Hello. > > Back in August 2011, a commit has been tagged to be included > into stable, this one: > > commit dccaf33fa37a1bc5d651baeb3bfeb6becb86597b > Author: Jiaying Zhang <jiayingz@xxxxxxxxxx> > Date: Fri Aug 19 19:13:32 2011 -0400 > > ext4: flush any pending end_io requests before DIO reads w/dioread_nolock > > There is a race between ext4 buffer write and direct_IO read with > dioread_nolock mount option enabled. The problem is that we clear > PageWriteback flag during end_io time but will do > uninitialized-to-initialized extent conversion later with dioread_nolock. > If an O_direct read request comes in during this period, ext4 will return > zero instead of the recently written data. > > This patch checks whether there are any pending uninitialized-to-initialized > extent conversion requests before doing O_direct read to close the race. > Note that this is just a bandaid fix. The fundamental issue is that we > clear PageWriteback flag before we really complete an IO, which is > problem-prone. To fix the fundamental issue, we may need to implement an > extent tree cache that we can use to look up pending to-be-converted extents. > > Signed-off-by: Jiaying Zhang <jiayingz@xxxxxxxxxx> > Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx> > Cc: stable@xxxxxxxxxx > > > There was one more ext4 commit at that time, which made its way into > stable but this one did not. > > I wonder if the reason for that was the fact that it needed a small > "backport" for 3.0, since in 3.1+ the code has been moved into another > file, and the context is slightly different. In that case, attached > is the "backport" which we use with 3.0.x since that time. > > Thanks! > > /mjt -- 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
