On 26.01.23 15:41, Claudio Imbrenda wrote:
On Thu, 26 Jan 2023 08:55:27 -0400
Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
On Thu, Jan 26, 2023 at 01:48:46PM +0100, David Hildenbrand wrote:
On 24.01.23 21:34, Jason Gunthorpe wrote:
Move the flags that should not/are not used outside gup.c and related into
mm/internal.h to discourage driver abuse.
To make this more maintainable going forward compact the two FOLL ranges
with new bit numbers from 0 to 11 and 16 to 21, using shifts so it is
explict.
Switch to an enum so the whole thing is easier to read.
Using a __bitwise type would be even better, but that requires quite some
adjustments ...
The primary leftover for FOLL_GET seems to be follow_page(). IIRC, there is
only one caller that doesn't pass FOLL_GET (s390). We could either add a new
function to "probe" that anything is mapped (IIRC that's the use case), or
simply ref+unref.
Is that code even safe as written? I don't really understand how it
yes (surprisingly) it is
can safely call lock_page() on something it doesn't have a reference
too ?
the code between lock_page and unlock_page will behave "properly" and
do nothing or at worst cause a tiny performance issue in the rare case
something changes between the follow_page and the page_lock, i.e. if
things are done on the wrong page.
What prevents the page from getting unmapped (MADV_DONTNEED), freed,
reallocated as a larger folio and the unlock_page() would target the
wrong bit? I think even while freeing a locked page we might run into
trouble ...
--
Thanks,
David / dhildenb
