On Fri, 11 Feb 2022, Rik van Riel wrote:
> Sometimes the page offlining code can leave behind a hwpoisoned clean
> page cache page. This can lead to programs being killed over and over
> and over again as they fault in the hwpoisoned page, get killed, and
> then get re-spawned by whatever wanted to run them.
Hi Rik,
This looks good. Some minor suggestions below:
>
> This is particularly embarrassing when the page was offlined due to
> having too many corrected memory errors. Now we are killing tasks
> due to them trying to access memory that probably isn't even corrupted.
I'd recommend deleting that paragraph entirely. It's a separate
question, and it is not necessarily an accurate assessment of that
question either: the engineers who set the thresholds for "too many
corrected errors" may not--in fact, probably *will not*--agree with your
feeling that the memory is still working and reliable!
>
> This problem can be avoided by invalidating the page from the page
> fault handler, which already has a branch for dealing with these
> kinds of pages. With this patch we simply pretend the page fault
> was successful if the page was invalidated, return to userspace,
> incur another page fault, read in the file from disk (to a new
> memory page), and then everything works again.
Very nice write-up here, it's rare that I get to read such a short, yet
clear explanation. Thank you for that. :)
>
> Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
>
> diff --git a/mm/memory.c b/mm/memory.c
> index c125c4969913..2300358e268c 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3871,11 +3871,16 @@ static vm_fault_t __do_fault(struct vm_fault *vmf)
> return ret;
>
> if (unlikely(PageHWPoison(vmf->page))) {
> - if (ret & VM_FAULT_LOCKED)
> + int poisonret = VM_FAULT_HWPOISON;
> + if (ret & VM_FAULT_LOCKED) {
How about changing those two lines to these three (note the newline
after the declaration):
vm_fault_t poison_ret = VM_FAULT_HWPOISON;
if (ret & VM_FAULT_LOCKED) {
...which should fix the krobot complaint, and the underscore is just a
very tiny readability improvement while we're there.
> + /* Retry if a clean page was removed from the cache. */
This is more cryptic than necessary, and in fact you've already provided
a write-up, so how about something like this, instead of the above:
/*
* Avoid refaulting on the same poisoned page
* forever: attempt to invalidate the page. If that
* succeeds, then pretend the page fault was successful,
* return to userspace, incur another page fault, read
* in the file from disk (to a new page),and then
* everything works again.
*/
> + if (invalidate_inode_page(vmf->page))
> + poisonret = 0;
> unlock_page(vmf->page);
> + }
> put_page(vmf->page);
> vmf->page = NULL;
> - return VM_FAULT_HWPOISON;
> + return poisonret;
> }
>
> if (unlikely(!(ret & VM_FAULT_LOCKED)))
>
>
> --
> All rights reversed.
Anyway, those are all documentation nits, except for the vm_fault_t,
which is a declaration nit :) , so I'm comfortable saying:
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
thanks,
--
John Hubbard
NVIDIA
