Re: [PATCH v2: [linux-4.14.y] ] dm cache: submit writethrough writes in parallel to origin and cache

[Greg KH]

On Thu, Jul 30, 2020 at 03:33:42PM -0500, John Donnelly wrote:
> From: Mike Snitzer <snitzer@xxxxxxxxxx>
> 
> Discontinue issuing writethrough write IO in series to the origin and
> then cache.
> 
> Use bio_clone_fast() to create a new origin clone bio that will be
> mapped to the origin device and then bio_chain() it to the bio that gets
> remapped to the cache device.  The origin clone bio does _not_ have a
> copy of the per_bio_data -- as such check_if_tick_bio_needed() will not
> be called.
> 
> The cache bio (parent bio) will not complete until the origin bio has
> completed -- this fulfills bio_clone_fast()'s requirements as well as
> the requirement to not complete the original IO until the write IO has
> completed to both the origin and cache device.
> 
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> 
> (cherry picked from commit 2df3bae9a6543e90042291707b8db0cbfbae9ee9)
> 
> Fixes: 4ec34f2196d125ff781170ddc6c3058c08ec5e73 (dm bio record:
> save/restore bi_end_io and bi_integrity )
> 
> 4ec34f21 introduced a mkfs.ext4 hang on a LVM device that has been
> modified with lvconvert --cachemode=writethrough.
> 
> CC:stable@xxxxxxxxxxxxxxx for 4.14.x .
> 
> Signed-off-by: John Donnelly <john.p.donnelly@xxxxxxxxxx>
> Reviewed-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@xxxxxxxxxx>
> 
> conflicts:
> 	drivers/md/dm-cache-target.c. -  Corrected usage of
> 	writethrough_mode(&cache->feature) that was caught by
> 	compiler, and removed unused static functions : writethrough_endio(),
> 	defer_writethrough_bio(), wake_deferred_writethrough_worker()
> 	that generated warnings.
> ---
>  drivers/md/dm-cache-target.c | 94
> ++++++++++++++++++--------------------------

Line wrapped?

>  1 file changed, 38 insertions(+), 56 deletions(-)
> 
> diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
> index 69cdb29ef6be..2d9566bfe08b 100644
> --- a/drivers/md/dm-cache-target.c
> +++ b/drivers/md/dm-cache-target.c
> @@ -1,5 +1,5 @@
>  /*
> - * Copyright (C) 2012 Red Hat. All rights reserved.
> + i Copyright (C) 2012 Red Hat. All rights reserved.

What happened here?

This patch can't be applied as-is :(

greg k-h