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Date: Fri, 19 Jul 2013 13:18:31 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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To: Konstantin Belousov <kostikbel@gmail.com>
Subject: Re: Deadlock in nullfs/zfs somewhere
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Cc: freebsd-fs@FreeBSD.org, Adrian Chadd <adrian@FreeBSD.org>
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on 18/07/2013 21:52 Konstantin Belousov said the following:
> There is VFS method VFS_SUSP_CLEAN, called when the suspension is
> lifted.  UFS uses it to clean the back-queue of work which were
> not performed during the suspend, mostly inactivate the postponed
> inactive vnodes.  ZFS probably does not need it, since it does
> not check for MNTK_SUSPEND, but if it starts care, there is a place
> to put the code.

I will keep this in mind.

> On the other hand, I believe that your patch is notoriously incomplete,
> because there should be a lot of threads which mutate ZFS mounts state
> and which do not call vn_start_write() around the mutations.  I.e.
> all ZFS top-level code which calls into ZFS ops and which is not
> coming from VFS.

I agree.  What I am trying to fix right now is VFS<->ZFS interaction.  I think
that ZFS<->ZFS should already be fine - it's protected by internal ZFS locking.
OTOH, perhaps my understanding of what you said is incomplete or incorrect,
because VFS suspension mechanism is completely unknown to me yet.


-- 
Andriy Gapon