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From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Dave Jiang <dave.jiang@intel.com>
Cc: linux-ext4@vger.kernel.org,
	Matthew Wilcox <mawilcox@microsoft.com>,
	linux-nvdimm@lists.01.org
Subject: Re: Help trying to use /dev/pmem for dax debugging?
Date: Thu, 9 Aug 2018 22:53:40 -0400	[thread overview]
Message-ID: <20180810025339.GB21087@thunk.org> (raw)
In-Reply-To: <30247efc-88f8-3e0b-fcd8-83801be5f041@intel.com>

On Tue, Jul 31, 2018 at 01:27:15PM -0700, Dave Jiang wrote:
> 
> On 7/31/2018 12:36 PM, Ross Zwisler wrote:
> > On Mon, Jul 30, 2018 at 07:53:12PM -0400, Theodore Y. Ts'o wrote:
> > > In newer kernels, it looks like you can't use /dev/pmem0 for DAX
> > > unless it's marked as being DAX capable.  This appears to require
> > > CONFIG_NVDIMM_PFN.  But when I tried to build a kernel with that
> > > configured, I get the following BUG:
> >
> > You're using the memmap kernel command line parameter to reserve normal
> > memory to be treated as normal memory, but you've also got kernel address
> > randomization turned on in your kernel config:
> > 
> > CONFIG_RANDOMIZE_BASE=y
> > CONFIG_RANDOMIZE_MEMORY=y
> > 
> > You need to turn these off for the memmap kernel command line parameter, else
> > the memory we're using could overlap with addresses used for other things.
> 
> I believe this issue was fixed a while back. Although we probably can see if
> that is the issue or something else.

I turned off RANDOMIZE_BASE and RANDOMIZE_MEMORY, but that didn't fix
my problem.

It turns out the problem was KASAN.  It looks like using memmap to
create test /dev/pmemX devices is not compatible with CONFIG_KASAN
being enabled.

So I have a workaround for now, but it seems this to be a bug in
KASAN, or at least an unfortunate interaction between KASAN and
NVDIMM_PFN.

						- Ted
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  reply	other threads:[~2018-08-10  2:53 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-30 23:53 Theodore Y. Ts'o
2018-07-31 19:36 ` Ross Zwisler
2018-07-31 20:27   ` Dave Jiang
2018-08-10  2:53     ` Theodore Y. Ts'o [this message]
2018-08-10 16:18       ` Dave Jiang
2018-08-10 17:28         ` Dan Williams

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