Matthew Wilcox <willy@xxxxxxxxxxxxx> writes:
> On Sat, Feb 27, 2021 at 01:11:35AM +0900, OGAWA Hirofumi wrote:
>> zero_user_segments() is used from __block_write_begin_int(), for
>> example like the following
>>
>> zero_user_segments(page, 4096, 1024, 512, 918)
>>
>> But new zero_user_segments() implements for HIGMEM + TRANSPARENT_HUGEPAGE
>> doesn't handle "start > end" case correctly, and hits BUG_ON(). (we
>> can fix __block_write_begin_int() instead though, it is the old and
>> multiple usage)
>
> Why don't we just take out the BUG_ON instead? The function doesn't
> actually do the wrong thing.
end1 is underflow with
if (start1 >= PAGE_SIZE) {
start1 -= PAGE_SIZE;
end1 -= PAGE_SIZE;
}
>> Also it calls kmap_atomic() unnecessary while start == end == 0.
>
> I'm OK with that. It always used to do that.
Old one is only one page, so it is always necessary if start1/end1 or
start2/end2 is valid range. But this one is multiple pages, so there are
completely unnecessary pages possibly.
>> Cc: <stable@xxxxxxxxxxxxxxx>
>> Signed-off-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
>
> Fixes: 0060ef3b4e6d ("mm: support THPs in zero_user_segments")
OK.
--
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
