Re: [PATCH 01/13] mm: Update ptep_get_lockless()s comment

[Nadav Amit]

On Oct 29, 2022, at 12:14 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Sat, Oct 29, 2022 at 11:58 AM Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>> Still not tested in any way, shape, or form. I decided I wanted to
>> send this one before booting into this and possibly blowing up ;^)
> 
> Well, it boots, and I see no difference with your PoC code.
> 
> It didn't fail for me before, it doesn't fail for me with those patches.
> 
> Again, the "it doesn't fail for me" is probably because I'm running it
> incorrectly, although for all I know there can also be hardware
> differences.

Please give me some time to test it. I presume you ran it with block ram
device (not tmpfs) and not on a virtual machine (which can affect besides
Intel/AMD implementation differences).

But even if your patches work and the tests pass, I am not sure it means
that everything is fine. I did not try to trigger a race with
shrink_page_list(), and doing that might be harder than the race I tried to
create before. I need to do some tracing to understand what I was missing in
my understanding of the shrink_page_list() - assuming that I am mistaken
about the buffers being potentially released.

I would note that my concern about releasing the buffers is partially driven
by to issues that were reported before [1]. I am actually not sure how they
were resolved.


[1] https://lore.kernel.org/all/20180103100430.GE4911@xxxxxxxxxxxxxx/