Re: [Qemu-devel] [PATCH v8 3/6] libnvdimm: add dax_dev sync flag

Pankaj Gupta
2019-05-13T17:32:49Z

Hi Dan,

While testing device mapper with DAX, I faced a bug with the commit:

commit ad428cdb525a97d15c0349fdc80f3d58befb50df
Author: Dan Williams <dan.j.williams@intel.com>
Date: Wed Feb 20 21:12:50 2019 -0800

When I reverted the condition to old code[1] it worked for me. I
am thinking when we map two different devices (e.g with device mapper), will
start & end pfn still point to same pgmap? Or there is something else which
I am missing here.

Note: I tested only EXT4.

[1]

- if (pgmap && pgmap->type == MEMORY_DEVICE_FS_DAX)
+ end_pgmap = get_dev_pagemap(pfn_t_to_pfn(end_pfn), NULL);
+ if (pgmap && pgmap == end_pgmap && pgmap->type == MEMORY_DEVICE_FS_DAX
+ && pfn_t_to_page(pfn)->pgmap == pgmap
+ && pfn_t_to_page(end_pfn)->pgmap == pgmap
+ && pfn_t_to_pfn(pfn) == PHYS_PFN(__pa(kaddr))
+ && pfn_t_to_pfn(end_pfn) == PHYS_PFN(__pa(end_kaddr)))
dax_enabled = true;
put_dev_pagemap(pgmap);

Thanks,
Pankaj