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Date: Wed, 11 Nov 2015 14:05:08 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Eugene Grosbein <eugen@grosbein.net>
Cc: Jeff Roberson <jeff@freebsd.org>, benno <benno@freebsd.org>,
 "freebsd-mips@freebsd.org" <freebsd-mips@freebsd.org>
Subject: Re: USB-related problem
Message-ID: <20151111120508.GZ2257@kib.kiev.ua>
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On Tue, Nov 10, 2015 at 02:25:09AM +0700, Eugene Grosbein wrote:
> On 09.11.2015 22:53, Adrian Chadd wrote:
> > ok, let's get it to hang, then break into ddb and do 'show
> > allthreads', 'show alllocks', 'bufvars' with my vfs_bio.c patch, etc.
> 
> I've re-read https://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug-deadlocks.html
> and rebuilt kernel with additional debugging and reproduced the problem again to supply
> more vfs lock info:

You have syncer running with the buffer arena mutex locked.  This probably
means that you have DIAGNOSTIC option turned on, do you ?  If yes,
set debug.vmem_check to zero, otherwise it just eats your anemic CPU.

Also, I am curious what is the value of vfs.unmapped_buf_allowed on
your platform.