svn commit: r294329 - in head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs: . sys

[Andriy Gapon]

On 20/01/2016 22:03, Alan Somers wrote:
> On Wed, Jan 20, 2016 at 2:20 AM, Andriy Gapon <avg at freebsd.org> wrote:
>> On 19/01/2016 19:20, Alan Somers wrote:
>>> The thing is, it never really worked in the first place.  Panics and
>>> deadlocks are so frequent that I don't think the feature was usable
>>> for anybody.
>>
>> The feature is perfectly usable for me.  I have never run into the problems that
>> you describe.  Why not fix the real bugs that you've run into?
> 
> Spectra Logic and iXSystems both experienced many problems with this.
> The worst is a deadlock that can be triggered simply by pulling a
> drive from a redundant pool when there exists a zvol anywhere in the
> system (see https://reviews.freebsd.org/D4998 for a quick way to
> reproduce).  Fixing it correctly would likely require far more time
> than I have available.  I just want the bugs to go away.  See that
> same code review for a change to make the feature optional.

I think that we all want all the bugs to go way.  One way to remove bugs is to
remove (disable) code that contains bugs.  That way the perfect bug-free
software is clearly achievable :-)  Unfortunately, that technique is not always
welcomed.

P.S.
I think that the real problem here is that a method of a geom must never drop
topology_lock.  In other words, the GEOM management code (like g_xxx() stuff in
geom_subr.c) expects that a topology can not change underneath it.  But
zvol_geom_access() clearly breaks that contract.

-- 
Andriy Gapon