On Mon, Aug 29, 2016 at 03:54:10PM +0800, Xiao Guangrong wrote: > > Hi Ross, > > Sorry for the delay, i just returned back from KVM Forum. > > On 08/20/2016 02:30 AM, Ross Zwisler wrote: > > On Fri, Aug 19, 2016 at 07:59:29AM -0700, Dan Williams wrote: > > > On Fri, Aug 19, 2016 at 4:19 AM, Xiao Guangrong > > > <guangrong.xiao@xxxxxxxxxxxxxxx> wrote: > > > > > > > > Hi Dan, > > > > > > > > Recently, Redhat reported that nvml test suite failed on QEMU/KVM, > > > > more detailed info please refer to: > > > > https://bugzilla.redhat.com/show_bug.cgi?id=1365721 > > > > > > > > The reason for this bug is that the memory region created by mmap() > > > > on the dax-based file was gone so that the region can not be found > > > > in /proc/self/smaps during the runtime. > > > > > > > > This is a simple way to trigger this issue: > > > > mount -o dax /dev/pmem0 /mnt/pmem/ > > > > vim /mnt/pmem/xxx > > > > then 'vim' is crashed due to segment fault. > > > > > > > > This bug can be reproduced on your tree, the top commit is > > > > 10d7902fa0e82b (dax: unmap/truncate on device shutdown), the kernel > > > > configure file is attached. > > > > > > > > Your thought or comment is highly appreciated. > > > > > > I'm going to be offline until Tuesday, but I will investigate when I'm > > > back. In the meantime if Ross or Vishal had an opportunity to take a > > > look I wouldn't say "no" :). > > > > I haven't been able to reproduce this vim segfault. I'm using QEMU v2.6.0, > > and the kernel commit you mentioned, and your kernel config. > > > > Here's my QEMU command line: > > > > sudo ~/qemu/bin/qemu-system-x86_64 /var/lib/libvirt/images/alara.qcow2 \ > > -machine pc,nvdimm -m 8G,maxmem=100G,slots=100 -object \ > > memory-backend-file,id=mem1,share,mem-path=/dev/pmem0,size=8G -device \ > > nvdimm,memdev=mem1,id=nv1 -smp 6 -machine pc,accel=kvm > > > > With this I'm able to mkfs the guest's /dev/pmem0, mount it with -o dax, and > > write a file with vim. > > Thanks for your test. That's strange... > > > > > Can you reproduce your results with a pmem device created via a memmap kernel > > command line parameter in the guest? You'll need to update your kernel > > config to enable CONFIG_X86_PMEM_LEGACY and CONFIG_X86_PMEM_LEGACY_DEVICE. > > > > Okay, i tested it with mmap=6G!10G, it failed too. So it looks like it's a > filesystem or DAX issue. > > More precisely, i figured out the root case that read() returns a wrong value > when it reaches the end of the file, following test case can trigger it: > > #include <stdlib.h> > #include <stdio.h> > #include <unistd.h> > #include <fcntl.h> > #include <sys/types.h> > #include <sys/stat.h> > > int main(int argc, char *argv[]) > { > char *filename; > > if (argc < 2) { > printf("arg: filename.\n"); > return -1; > } > > filename = argv[1]; > printf("test on %s.\n", filename); > > int fd = open(filename, O_RDWR); > > if (fd < 0) { > perror("open"); > return -1; > } > > int count = 0; > > while (1) { > ssize_t ret; > char buf; > > ret = read(fd, &buf, sizeof(buf)); > if (ret < 0) { > perror("READ"); > return -1; > } > > if (ret == 0) > break; > if (ret != sizeof(buf)) { > printf("Count %x Ret %lx sizeof(buf) %lx.\n", > count, ret, sizeof(buf)); > return -1; > } > > count++; > printf("%c", buf); > } > > printf("\n Good Read.\n"); > return 0; > } > > > > It will fail at "ret != sizeof(buf)", for example, the error output on my > test env is: > Count 1000 Ret 22f84200 sizeof(buf) 1. Can you please verify that you are using "usable" memory for your memmap? All the details are here: https://nvdimm.wiki.kernel.org/how_to_choose_the_correct_memmap_kernel_parameter_for_pmem_on_your_system My guess is that Boaz was correct, and that your memmap is off using addresses that don't actually map to memory. - Ross -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
