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Date: Fri, 10 Aug 2018 09:16:26 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Rick Macklem <rmacklem@uoguelph.ca>
Cc: "freebsd-current@FreeBSD.org" <freebsd-current@FreeBSD.org>, peter@holm.cc
Subject: Re: ffs_truncate3 panics
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On Thu, Aug 09, 2018 at 08:38:50PM +0000, Rick Macklem wrote:
> I did notice that my code locks the vnode first and then calls vn_start_write()
>  for the vn_extattr_set() calls, whereas the syscall code locks the vnode after the vn_start_write() call.
> 
> Does that matter?

Yes, it matter.  It would cause deadlocks when corresponding filesystem
is suspended in parallel with NFSD activities.  vn_start_write() is a lock,
and the correct lock order is vn_start_write()->vnode lock.