Re: read corruption with qemu master io_uring engine / linux master / btrfs(?)

[Filipe Manana <fdmanana@kernel.org>]

On Thu, Jun 30, 2022 at 10:08:18PM +0900, Dominique MARTINET wrote:
> Filipe Manana wrote on Thu, Jun 30, 2022 at 01:51:24PM +0100:
> > > Please ask if there's any infos I could get you.
> > 
> > Ok, maybe it's page fault related or there's something else besides page faults
> > involved.
> > 
> > Can you dump the subvolume tree like this:
> > 
> > btrfs inspect-internal dump-tree -t 5 /dev/sda 2>&1 | xz -9 > dump.xz
> > 
> > Here the 5 is the ID of the default subvolume. If the test file is on
> > a different subvolume, you'll need to replace 5 with the subvolume's ID.
> 
> Sure thing.
> 
> It's 2MB compressed:
> https://gaia.codewreck.org/local/tmp/dump-tree.xz

Ok, the file has a mix of compressed and non-compressed extents.

This may prevent the short reads (not tested yet):

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 7a54f964ff37..42fb56ed0021 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7684,7 +7684,7 @@ static int btrfs_dio_iomap_begin(struct inode *inode, loff_t start,
        if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags) ||
            em->block_start == EXTENT_MAP_INLINE) {
                free_extent_map(em);
-               ret = -ENOTBLK;
+               ret = (flags & IOMAP_NOWAIT) ? -EAGAIN : -ENOTBLK;
                goto unlock_err;
        }
 
Can you give it a try?

Thanks.

> 
> 
> > This is just to look at the file extent layout.
> > Also, then tell me what's the inode number of the file (or just its name,
> > and I'll find out its inode number), and an example file offset and read
> > length that triggers a short read, so that I know where to look at.
> 
> There's just a single file in that subvolume, inode 257
> 
> > And btw, that dump-tree command will dump all file names, directory names
> > and xattr names and values (if they are human readable) - so if privacy is
> > a concern here, just pass --hide-names to the dump-tree command.
> 
> (thanks for the warning)
> -- 
> Dominique