[dm-devel] [PATCH v2] dm thin: Fix bug wrt FUA request completion

[Mike Snitzer]

On Thu, Feb 14 2019 at  6:21pm -0500,
Nikos Tsironis <ntsironis at arrikto.com> wrote:

> When provisioning a new data block for a virtual block, either because
> the block was previously unallocated or because we are breaking sharing,
> if the whole block of data is being overwritten the bio that triggered
> the provisioning is issued immediately, skipping copying or zeroing of
> the data block.
> 
> When this bio completes the new mapping is inserted in to the pool's
> metadata by process_prepared_mapping(), where the bio completion is
> signaled to the upper layers.
> 
> This completion is signaled without first committing the metadata. If
> the bio in question has the REQ_FUA flag set and the system crashes
> right after its completion and before the next metadata commit, then the
> write is lost despite the REQ_FUA flag requiring that I/O completion for
> this request is only signaled after the data has been committed to
> non-volatile storage.
> 
> Fix this by deferring the completion of overwrite bios, with the REQ_FUA
> flag set, after the metadata has been committed.
> 
> Signed-off-by: Nikos Tsironis <ntsironis at arrikto.com>
> ---
>  drivers/md/dm-thin.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 50 insertions(+), 5 deletions(-)
> 
> Changes in v2:
>   - Add missing bio_list_init() in pool_create()
> 
> v1: https://www.redhat.com/archives/dm-devel/2019-February/msg00064.html

Thanks a lot for your fix.  Amazing this was missed until now.

I staged your fix in linux-next and will be sending it to Linus
tomorrow (you'll note I tweaked the subject and header very slightly):

https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-5.0&id=4ae280b4ee3463fa57bbe6eede26b97daff8a0f1

Thanks again,
Mike