From: "Theodore Y. Ts'o" Subject: Re: Help trying to use /dev/pmem for dax debugging? Date: Thu, 9 Aug 2018 22:53:40 -0400 Message-ID: <20180810025339.GB21087@thunk.org> References: <20180730235312.GA5089@thunk.org> <20180731193642.GA3473@linux.intel.com> <30247efc-88f8-3e0b-fcd8-83801be5f041@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Matthew Wilcox , linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org To: Dave Jiang Return-path: Content-Disposition: inline In-Reply-To: <30247efc-88f8-3e0b-fcd8-83801be5f041-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" List-Id: linux-ext4.vger.kernel.org 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