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

[John Donnelly <john.p.donnelly@oracle.com>]

On 7/31/20 1:54 AM, Greg KH wrote:
> On Thu, Jul 30, 2020 at 03:33:42PM -0500, John Donnelly wrote:
>> From: Mike Snitzer <snitzer@redhat.com>
>>
>> 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@redhat.com>
>>
>> (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@vger.kernel.org for 4.14.x .
>>
>> Signed-off-by: John Donnelly <john.p.donnelly@oracle.com>
>> Reviewed-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>
>>
>> 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?

  ummm .. that is weird

> 
>>   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?

  spurious character from vi ;-(

> 
> This patch can't be applied as-is :(
> 
> greg k-h
> 

  I will repost next week Thank you.