Re: XFS crash consistency bug : Loss of fsynced metadata operation

Dave Chinner
2018-03-16T00:21:22Z

On Thu, Mar 15, 2018 at 11:32:07AM +0100, Lukas Czerner wrote:
>
> And where the "cdcd" data is comming from ? Not from the
>
> "pwrite -S 1 0 64k"
>
> that's producing "0101".

Ah, too much context switching. Makes me look like the village
idiot...

Ok, I just spent some time looking at this in detail (event traces,
etc) and it is indeed as the test describes - an whole delalloc
extent allocation on partial overwrite. THe partial overwrite is
triggered by the fpunch/fzero code, and it appears the delalloc
converison is not paying attention to the start offset of the
writeback:

xfs_writepage: dev 7:0 ino 0x7603 pgoff 0xf000 size 0x10000 delalloc 1
.....
xfs_alloc_near_greater: dev 7:0 agno 0 agbno 3784 minlen 16 maxlen 16
.....
xfs_write_extent: dev 7:0 ino 0x7603 offset 0 block 3784 count 16 flag 0

IOWs, as I've said from the start (based on the test description)
this has nothing to do with the corruption issue CrashMonkey is
creating.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com