On 10/15/26 12:16 AM, Ricardo B. Marlière (SUSE) wrote:
> remap_region() checks that the destination region is free before mapping
> it, but not the preamble region placed right before it, so mapping the
> preamble can intermittently fail with EEXIST:
>
> # Failed to map dest preamble region: File exists
> not ok 15 5MB mremap - Source 1MB-aligned, Dest 1MB-aligned with 40MB
> Preamble
>
> This happens when the kernel's heap ASLR (arch_randomize_brk()) lands the
> process heap inside that unchecked range. Confirmed by correlating
> brk(NULL) at startup with pass/fail across 60 runs: every failure had brk
> land inside that range.
>
> Fix it by including the preamble in the free-region check.
>
> Signed-off-by: Ricardo B. Marlière (SUSE) <[email protected]>
> ---
Just wondering, should this have a Fixes: tag as well?
Other than that, LGTM.
Reviewed-by: Sarthak Sharma <[email protected]>
> Hi, this sporadic issue has been found in openSUSE CI:
>
> https://openqa.opensuse.org/tests/6270334/logfile?filename=serial_terminal.txt#line-6760
> ---
> tools/testing/selftests/mm/mremap_test.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/mremap_test.c
> b/tools/testing/selftests/mm/mremap_test.c
> index 131d9d6db867..8d4fa3025a9d 100644
> --- a/tools/testing/selftests/mm/mremap_test.c
> +++ b/tools/testing/selftests/mm/mremap_test.c
> @@ -1006,8 +1006,10 @@ static long long remap_region(struct config c,
> unsigned int threshold_mb,
> if (!((unsigned long long) addr & c.dest_alignment))
> addr = (void *) ((unsigned long long) addr | c.dest_alignment);
>
> - /* Don't destroy existing mappings unless expected to overlap */
> - while (!is_remap_region_valid(addr, c.region_size) && !c.overlapping) {
> + /* Don't destroy existing mappings unless expected to overlap. */
> + while (!is_remap_region_valid(addr - c.dest_preamble_size,
> + c.dest_preamble_size + c.region_size) &&
> + !c.overlapping) {
> /* Check for unsigned overflow */
> tmp_addr = addr + c.dest_alignment;
> if (tmp_addr < addr) {
>
> ---
> base-commit: 0fcb05b72344f40806cbe810de8872f1698bf053
> change-id: 20261014-selftests-mm-mremap_preamble-5f98ad625f93
>
> Best regards,
> --
> Ricardo B. Marlière (SUSE) <[email protected]>
