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Date:      Sat, 18 May 2024 22:59:13 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 279138] NFS and NFSUPG and BUFWAIT
Message-ID:  <bug-279138-227-Osv91KLJOU@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-279138-227@https.bugs.freebsd.org/bugzilla/>
References:  <bug-279138-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D279138

--- Comment #3 from Konstantin Belousov <kib@FreeBSD.org> ---
The first LoR looks as a false positive, mostly.  It is readdirplus doing
scan of the directory, and then querying the attributes of each found entry'
node, except dotdot.  So the lock order is parent vnode -> (it's buffers) ->
child vnode, as expected by VFS.

I said "mostly" because server can do the directory move like from A->B to
B->A while client is not aware, and I am not completely sure that our clien=
t-
side invalidations would avoid tricking in this situation.  But this is very
unlikely.

For the second LoR, nfsupg->bufwait, the reported order is right.  I wonder
where the reversed order was recorded.

That said, to diagnose the problem, you need to gather the information list=
ed
in the developer's handbook, debugging kernels, debugging deadlocks:
https://docs.freebsd.org/en/books/developers-handbook/kerneldebug/#kernelde=
bug-deadlocks

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