svn commit: r340097 - in head/sys: kern sys

[Hans Petter Selasky]

On 11/3/18 4:43 AM, Matt Macy wrote:
> Author: mmacy
> Date: Sat Nov  3 03:43:32 2018
> New Revision: 340097
> URL: https://svnweb.freebsd.org/changeset/base/340097
> 
> Log:
>    Convert epoch to read / write records per cpu
>    
>    In discussing D17503 "Run epoch calls sooner and more reliably" with
>    sbahra@ we came to the conclusion that epoch is currently misusing the
>    ck_epoch API. It isn't safe to do a "write side" operation (ck_epoch_call
>    or ck_epoch_poll) in the middle of a "read side" section. Since, by definition,
>    it's possible to be preempted during the middle of an EPOCH_PREEMPT
>    epoch the GC task might call ck_epoch_poll or another thread might call
>    ck_epoch_call on the same section. The right solution is ultimately to change
>    the way that ck_epoch works for this use case. However, as a stopgap for
>    12 we agreed to simply have separate records for each use case.
>    
>    Tested by: pho@
>    
>    MFC after:	3 days

^^^ not yet MFC'ed - any reason why not?
--HPS