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Date:      Thu, 9 May 2013 13:56:33 -0700
From:      Marcel Moolenaar <marcel@xcllnt.net>
To:        attilio@FreeBSD.org
Cc:        svn-src-head@freebsd.org, svn-src-all@freebsd.org, Marcel Moolenaar <marcel@freebsd.org>, src-committers@freebsd.org
Subject:   Re: svn commit: r250411 - in head/sys: conf kern sys
Message-ID:  <CC06FD75-868C-40B3-9C10-D66B56327803@xcllnt.net>
In-Reply-To: <CAJ-FndBY%2ByuUdvO4zP3kf2W4gDvB-uih19bqdmkFW3E4NcrHtw@mail.gmail.com>
References:  <201305091628.r49GSI33039873@svn.freebsd.org> <CAJ-FndBY%2ByuUdvO4zP3kf2W4gDvB-uih19bqdmkFW3E4NcrHtw@mail.gmail.com>

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On May 9, 2013, at 9:46 AM, Attilio Rao <attilio@freebsd.org> wrote:

> On Thu, May 9, 2013 at 6:28 PM, Marcel Moolenaar <marcel@freebsd.org> =
wrote:
>> Author: marcel
>> Date: Thu May  9 16:28:18 2013
>> New Revision: 250411
>> URL: http://svnweb.freebsd.org/changeset/base/250411
>>=20
>> Log:
>>  Add option WITNESS_NO_VNODE to suppress printing LORs between VNODE
>>  locks. To support this, VNODE locks are created with the LK_IS_VNODE
>>  flag. This flag is propagated down using the LO_IS_VNODE flag.
>>=20
>>  Note that WITNESS still records the LOR. Only the printing and the
>>  optional entering into the kernel debugger is bypassed with the
>>  WITNESS_NO_VNODE option.
>=20
> This is the wrong way to deal with such problem and I avoided to do
> something like that on purpose.

I disagree. We have known LOR messages between VNODE locks that
pollute the console and so far we haven't fixed the root cause
in some form or shape. Silencing this known case is good to
maximize the attention LORs need to be given while still have
witness involved to catch locking problems with vnodes that are
of a different nature.

>=20
> The way to fix this is to implement LK_NOWITNESS on a per-lock basis
> into lockmgr, propagate the same concept to the vn_lock() (which
> should be basically done automatically) and finally identify the
> false-positive case and commit for them explicitely LK_NOWITNESS on a
> per-call basis, explaining in detail why the single case reported is a
> false-positive.

This is worse. You want witness involved.

> Please revert this patch asap.

This change does not inhibit people from fixing the problem at the
root cause, and in the mean time maximize witness' effectiveness.
Calling for a backout is unwarranted and unnecessarily aggressive.

--=20
Marcel Moolenaar
marcel@xcllnt.net





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