We were trying to simulate pmem errors in an environment where a DAX filesystem is used (ext4 although I suspect it does not matter). The sequence attempted on a DAX filesystem is: - Populate a file in the DAX filesystem - mmap the file - madvise(MADV_HWPOISON)
The madvise operation fails with EFAULT. This appears to come from get_user_pages() as there are no struct pages for such mappings? The idea is to make sure an application can recover from such errors by hole punching and repopulating with another page. A couple questions: It seems like madvise(MADV_HWPOISON) is not going to work (ever?) in such situations. If so, should we perhaps add a IS_DAX like check and return something like EINVAL? Or, at least document expected behavior? If madvise(MADV_HWPOISON) will not work, how can one inject errors to test error handling code? -- Mike Kravetz
