Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes:
> On Thu, 08 Feb 2018 12:30:45 +0000 Punit Agrawal <punit.agrawal@xxxxxxx> wrote:
>
>> >
>> > So I don't think that the above test result means that errors are properly
>> > handled, and the proposed patch should help for arm64.
>>
>> Although, the deviation of pud_huge() avoids a kernel crash the code
>> would be easier to maintain and reason about if arm64 helpers are
>> consistent with expectations by core code.
>>
>> I'll look to update the arm64 helpers once this patch gets merged. But
>> it would be helpful if there was a clear expression of semantics for
>> pud_huge() for various cases. Is there any version that can be used as
>> reference?
>
> Is that an ack or tested-by?
>
> Mike keeps plaintively asking the powerpc developers to take a look,
> but they remain steadfastly in hiding.
Cc'ing linuxppc-dev is always a good idea :)
> Folks, this patch fixes a BUG and is marked for -stable. Can we please
> prioritize it?
It's not crashing for me (on 4.16-rc1):
# ./huge-poison
Poisoning page...once
Poisoning page...once again
madvise: Bad address
And I guess the above is the expected behaviour?
Looking at the function trace it looks like the 2nd madvise is going
down reasonable code paths, but I don't know for sure:
8) | SyS_madvise() {
8) | capable() {
8) | ns_capable_common() {
8) 0.094 us | cap_capable();
8) 0.516 us | }
8) 1.052 us | }
8) | get_user_pages_fast() {
8) 0.354 us | gup_pgd_range();
8) | get_user_pages_unlocked() {
8) 0.050 us | down_read();
8) | __get_user_pages() {
8) | find_extend_vma() {
8) | find_vma() {
8) 0.148 us | vmacache_find();
8) 0.622 us | }
8) 1.064 us | }
8) 0.028 us | arch_vma_access_permitted();
8) | follow_hugetlb_page() {
8) | huge_pte_offset() {
8) 0.128 us | __find_linux_pte();
8) 0.580 us | }
8) 0.048 us | _raw_spin_lock();
8) | hugetlb_fault() {
8) | huge_pte_offset() {
8) 0.034 us | __find_linux_pte();
8) 0.434 us | }
8) 0.028 us | is_hugetlb_entry_migration();
8) 0.032 us | is_hugetlb_entry_hwpoisoned();
8) 2.118 us | }
8) 4.940 us | }
8) 7.468 us | }
8) 0.056 us | up_read();
8) 8.722 us | }
8) + 10.264 us | }
8) + 12.212 us | }
cheers
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