On 10/25/24 19:12, Lorenzo Stoakes wrote:
> On Wed, Oct 23, 2024 at 05:24:40PM +0100, Lorenzo Stoakes wrote:
>> Implement a new lightweight guard page feature, that is regions of userland
>> virtual memory that, when accessed, cause a fatal signal to arise.
>
> <snip>
>
> Hi Andrew - Could you apply the below fix-patch? I realise we must handle
> fatal signals and conditional rescheduling in the vector_madvise() special
> case.
>
> Thanks!
>
> ----8<----
> From 546d7e1831c71599fc733d589e0d75f52e84826d Mon Sep 17 00:00:00 2001
> From: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> Date: Fri, 25 Oct 2024 18:05:48 +0100
> Subject: [PATCH] mm: yield on fatal signal/cond_sched() in vector_madvise()
>
> While we have to treat -ERESTARTNOINTR specially here as we are looping
> through a vector of operations and can't simply restart the entire
> operation, we mustn't hold up fatal signals or RT kernels.
For plain madvise() syscall returning -ERESTARTNOINTR does the right thing
and checks fatal_signal_pending() before returning, right?
Uh actually can we be just returning -ERESTARTNOINTR or do we need to use
restart_syscall()?
> ---
> mm/madvise.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 48eba25e25fe..127aa5d86656 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1713,8 +1713,14 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
> * we have already rescinded locks, it should be no problem to
> * simply try again.
> */
> - if (ret == -ERESTARTNOINTR)
> + if (ret == -ERESTARTNOINTR) {
> + if (fatal_signal_pending(current)) {
> + ret = -EINTR;
> + break;
> + }
> + cond_resched();
Should be unnecessary as we're calling an operation that takes a rwsem so
there are reschedule points already. And with lazy preempt hopefully
cond_resched()s will become history, so let's not add more only to delete later.
> continue;
> + }
> if (ret < 0)
> break;
> iov_iter_advance(iter, iter_iov_len(iter));
> --
> 2.47.0
