On 8/21/21 4:25 PM, Al Viro wrote:

On Sat, Aug 21, 2021 at 03:24:28PM +0100, Pavel Begunkov wrote:

quoted

On 8/12/21 9:40 PM, Pavel Begunkov wrote:

quoted

For the bug description see 2/2. As mentioned there the current problems
is because of generic_write_checks(), but there was also a similar case
fixed in 5.12, which should have been triggerable by normal
write(2)/read(2) and others.

It may be better to enforce reexpands as a long term solution, but for
now this patchset is quickier and easier to backport.

We need to do something with this, hopefully soon.

I still don't like that approach ;-/  If anything, I would rather do
something like this, and to hell with one extra word on stack in
several functions; at least that way the semantics is easy to describe.

Pavel suggested this very approach initially as well when we discussed
it, and if you're fine with the extra size_t, it is by far the best way
to get this done and not have a wonky/fragile API.

-- 
Jens Axboe