Re: Is MADV_HWPOISON supposed to work only on faulted-in pages?

On Tue, Feb 14, 2017 at 04:41:29PM +0100, Jan Stancek wrote:

Hi,

code below (and LTP madvise07 [1]) doesn't produce SIGBUS,
unless I touch/prefault page before call to madvise().

Is this expected behavior?

Thank you for reporting.

madvise(MADV_HWPOISON) triggers page fault when called on the address
over which no page is faulted-in, so I think that SIGBUS should be
called in such case.

But it seems that memory error handler considers such a page as "reserved
kernel page" and recovery action fails (see below.)

  [  383.371372] Injecting memory failure for page 0x1f10 at 0x7efcdc569000
  [  383.375678] Memory failure: 0x1f10: reserved kernel page still referenced by 1 users
  [  383.377570] Memory failure: 0x1f10: recovery action for reserved kernel page: Failed

I'm not sure how/when this behavior was introduced, so I try to understand.
IMO, the test code below looks valid to me, so no need to change.

Thanks,
Naoya Horiguchi

Thanks,
Jan

[1] https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/madvise/madvise07.c

-------------------- 8< --------------------
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>

int main(void)
{
	void *mem = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE,
			MAP_ANONYMOUS | MAP_PRIVATE /*| MAP_POPULATE*/,
			-1, 0);

	if (mem == MAP_FAILED)
		exit(1);

	if (madvise(mem, getpagesize(), MADV_HWPOISON) == -1)
		exit(1);

	*((char *)mem) = 'd';

	return 0;
}
-------------------- 8< --------------------

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