Thanks Michal.
On 3/24/2022 6:18 PM, Michal Hocko wrote:
> On Wed 23-03-22 20:54:09, Charan Teja Kalla wrote:
>> This reverts commit 08095d6310a7 ("mm: madvise: skip unmapped vma holes
>> passed to process_madvise") as process_madvise() fails to return exact
>> processed bytes at other cases too. As an example: if the
>> process_madvise() hits mlocked pages after processing some initial bytes
>> passed in [start, end), it just returns EINVAL though some bytes are
>> processed. Thus making an exception only for ENOMEM is partially fixing
>> the problem of returning the proper advised bytes.
>>
>> Thus revert this patch and return proper bytes advised, if there any,
>> for all the error types in the following patch.
>
> I do agree with the revert. I am not sure the above really is a proper
> justification though. 08095d6310a7 was changing one (arguably) dubious
> semantic by another one without a proper justification and wider
> consensus which I would expect from a patch which changes an existing
> semantic. Not to mention it being marked for stable tree.
Thanks for pointing this out. Since 08095d6310a7 is marked for stable
tree, doing the same for this change.
Cc: <stable@xxxxxxxxxxxxxxx> # 5.10+
>
> But let's not nit pick on that now. Let's send this revert ASAP and use
> some more time to discuss the semantic and whether any change is really
> required.
>
>> Signed-off-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
>
Thanks for the quick ack.
>> ---
>> mm/madvise.c | 9 +--------
>> 1 file changed, 1 insertion(+), 8 deletions(-)
>>
>> diff --git a/mm/madvise.c b/mm/madvise.c
>> index 39b712f..0d8fd17 100644
>> --- a/mm/madvise.c
>> +++ b/mm/madvise.c
>> @@ -1433,16 +1433,9 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
>>
>> while (iov_iter_count(&iter)) {
>> iovec = iov_iter_iovec(&iter);
>> - /*
>> - * do_madvise returns ENOMEM if unmapped holes are present
>> - * in the passed VMA. process_madvise() is expected to skip
>> - * unmapped holes passed to it in the 'struct iovec' list
>> - * and not fail because of them. Thus treat -ENOMEM return
>> - * from do_madvise as valid and continue processing.
>> - */
>> ret = do_madvise(mm, (unsigned long)iovec.iov_base,
>> iovec.iov_len, behavior);
>> - if (ret < 0 && ret != -ENOMEM)
>> + if (ret < 0)
>> break;
>> iov_iter_advance(&iter, iovec.iov_len);
>> }
>> --
>> 2.7.4
>
