From: Dave Jiang Subject: Re: Help trying to use /dev/pmem for dax debugging? Date: Fri, 10 Aug 2018 09:18:11 -0700 Message-ID: <4222843a-13ea-e88f-ca74-4e3fe53b4105@intel.com> References: <20180730235312.GA5089@thunk.org> <20180731193642.GA3473@linux.intel.com> <30247efc-88f8-3e0b-fcd8-83801be5f041@intel.com> <20180810025339.GB21087@thunk.org> 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: "Theodore Y. Ts'o" Return-path: In-Reply-To: <20180810025339.GB21087-AKGzg7BKzIDYtjvyW6yDsg@public.gmane.org> Content-Language: en-US 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 08/09/2018 07:53 PM, Theodore Y. Ts'o wrote: > 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. Thanks Ted. I have updated the wiki Ross mentioned to reflect that.