> Hello,
>
> Block layer didn't consider failfast status while merging requests and
> it led to premature failure of normal (non-failfast) IOs. Niel
> Lambrechts could trigger the problem semi-reliably on ext4 when
> resuming from STR. ext4 uses readahead when reading inodes and
> combined with the deterministic extra SATA PHY exception cycle during
> resume on the specific configuration, non-readahead inode read would
> fail causing ext4 errors. Please read the following thread for
> details.
>
>
http://lkml.org/lkml/2009/5/23/21
>
> This patchset contains the following four patches to fix the problem.
>
> 0001-block-don-t-merge-requests-of-different-failfast-se.patch
> 0002-block-use-the-same-failfast-bits-for-bio-and-reques.patch
> 0003-block-implement-mixed-merge-of-different-failfast-r.patch
> 0004-scsi-block-update-SCSI-to-handle-mixed-merge-failur.patch
>
> 0001 disallows merge between requests with different failfast
> settings. This one is the quick fix and should go into 2.6.31 and
> later to -stable as the bug is pretty serious and may lead to data
> loss.
>
> 0002 preps for later changes.
>
> 0003-0004 implements and applies mixed merge. Requests of different
> failfast settings are merged as before but failure handling is updated
> such that parts which shouldn't fail without retrial are properly
> retried.
>
> I spent quite some time thinking about and testing it but I'd really
> like more pairs of eyes on this patchset as dangerous bugs can go
> unnoticed for quite a while in this area (anyone knows when the
> failfast bug was introduced?).
