Re: vfs.zfs.vol.recursive completely broken, time to remove?

On Wed, Sep 29, 2021 at 12:10 AM Andriy Gapon <avg@freebsd.org> wrote:
>
>
> It seems that while previously there could sometimes be a deadlock with
> vfs.zfs.vol.recursive=1, now it is guaranteed.
>
> There was an OpenZFS change to use a pool of threads for vdev opening (to
> parallelize / speed up).  When such a thread opens a zvol it needs to acquire
> spa_namespace_lock.  But the lock is already held by a thread requesting the
> operation such as a thread doing zpool import (spa_load).
> So, it's an obvious deadlock: the main thread is waiting for the workers while
> holding the namespace lock, at least one of the workers is blocked on the same lock.

The last time I tried that there was pushback from a lot of different
people.  I think we need to fix it instead.  Here's the beginning of
that flame war.
https://docs.freebsd.org/cgi/getmsg.cgi?fetch=1031189+0+archive/2016/svn-src-all/20160124.svn-src-all