[dm-devel] [PATCH v2] dm mpath: Add timeout mechanism for queue_if_no_path

[Gabriel Krisman Bertazi]

Mike Snitzer <snitzer at redhat.com> writes:

> On Mon, Jan 13 2020 at  5:41P -0500,
> Gabriel Krisman Bertazi <krisman at collabora.com> wrote:
>
>> From: Anatol Pomazau <anatol at google.com>
>> 
>> Add a configurable timeout mechanism to disable queue_if_no_path without
>> assistance from multipathd.  In reality, this reimplements the
>> no_path_retry mechanism from multipathd in kernel space, which is
>> interesting to prevent processes from hanging indefinitely in cases
>> where the daemon might be unable to respond, after a failure or for
>> whatever reason.
>> 
>> Despite replicating the policy configuration on kernel space, it is
>> quite an important case to prevent IOs from hanging forever, waiting for
>> userspace to behave correctly.
>> 
>> v2:
>>   - Use a module parameter instead of configuring per table
>>   - Simplify code
>> 
>> Co-developed-by: Frank Mayhar <fmayhar at google.com>
>> Signed-off-by: Frank Mayhar <fmayhar at google.com>
>> Co-developed-by: Bharath Ravi <rbharath at google.com>
>> Signed-off-by: Bharath Ravi <rbharath at google.com>
>> Co-developed-by: Khazhismel Kumykov <khazhy at google.com>
>> Signed-off-by: Khazhismel Kumykov <khazhy at google.com>
>> Signed-off-by: Anatol Pomazau <anatol at google.com>
>> Co-developed-by: Gabriel Krisman Bertazi <krisman at collabora.com>
>> Signed-off-by: Gabriel Krisman Bertazi <krisman at collabora.com>
>
> All these tags seem rather excessive (especially in that you aren't cc
> most of them on the submission).  Please review/scrub.  Just seems odd
> that so many had a hand in this relatively small patch.

Hey,

I removed some of the Cc's because those emails addresses were bouncing.
Still, I kept the lines for credits.  I got the bounces when sending v1.

> The Signed-off-by for anatol at google.com seems wrong, or did Anatol
> shephard this patch at some point?  Or did you mean Reviewed-by?
> Something else?

Anatol was the main author, as listed in the From: header.  This
seems correct with regard to the ordering rules of
Documentation/process/submitting-patches.rst, in particular the second
example, (Example of a patch submitted by a Co-developed-by: author::).

Am I missing something?

>
> Anyway, if in the end you hold these tags to reflect the development
> evolution of this patch then so be it ;)
>
> I've reviewed the changes and found various things I felt were
> worthwhile to modify.  Summary:
>
> - included missing <linux/timer.h>
> - added MODULE_PARM_DESC
> - moved new functions to reduce needed forward declarations
> - tweaked queue_if_no_path_timeout_work's DMWARN message
> - added lockdep_assert_held to enable_nopath_timeout
> - renamed static queue_if_no_path_timeout to queue_if_no_path_timeout_secs
> - use READ_ONCE when accessing queue_if_no_path_timeout_secs
>

The changes you made look good to me and your version of the patch
passes my testcase.

-- 
Gabriel Krisman Bertazi