persistent reservation behaviour with dm-multipath

[Christophe Varoqui <christophe.varoqui@free.fr>]

The current dm-multipath behaviour is currently a potent data corrupter
on Persistant Reservation-based clusters sharing multipaths with the
queue_if_no_path feature on (Clariion, Storageworks, ...).

Consider the following scenario :

- Node A take a write-exclusive persistent reservation on LU
- Node B submits a write io to LU, which is a sda-sdb multipath
- B dm_multipath routes the wio to sda, the wio is failed, the path is
marked failed
- B dm_multipath routes the wio to sdb, the wio is failed, the last
path is marked failed
- B queues the wio because of the queue_if_no_path feature. Process
submitting the wio is stuck in D-state.
- A releases the reservation. Queued wios are unqueued, corrupting the
data on LU.

I suspect wio returning a "reservation conflict" status should never be
queued.

DM suspend/resume on the multipath devmap effectively flushes the queue,
but this solution leaves a window open for data corruption, between io
enqueue and user-space driven queue flush.

Is there work in progress to address this issue yet ? What's would be an
acceptable solution design (for example Mike Christie suggested in Aug
2005 a scsi-to-blk error translation patch, which got nowhere) ?

Regards,
cvaroqui

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