[dm-devel] block: be more careful about status in __bio_chain_endio

[Christoph Hellwig]

On Tue, Jun 11, 2019 at 10:56:42PM -0400, John Dorminy wrote:
> I believe the second of these might, but is not guaranteed to,
> preserve the first error observed in a child; I believe if you want to
> definitely save the first error you need an atomic.

Is there any reason not to simply use a cmpxchg?  Yes, it is a
relatively expensive operation, but once we are chaining bios we are out
of the super hot path anyway.  We do something similar in xfs and iomap
already.