On Fri, Jan 08, 2021 at 02:22:51PM -0800, Tony Luck wrote:
> futex_wait_setup() first tries to read the user value with page faults
> disabled (because it holds a lock, and so cannot sleep). If that read
> fails it drops the lock and tries again.
>
> But there are now two reasons why the user space read can fail. Either:
> 1) legacy case of a page fault, in which case it is reasonable to retry
> 2) machine check on the user address, bad idea to re-read
>
> Add some infrastructure to differentiate these cases.
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -2658,6 +2658,9 @@ static int futex_wait_setup(u32 __user *uaddr, u32 val,
> unsigned int flags,
> if (ret) {
> queue_unlock(*hb);
>
> + if (arch_memory_failure(uaddr))
> + return ret;
> +
> ret = get_user(uval, uaddr);
> if (ret)
> return ret;
I think this is horrid; why can't we have it return something different
then -EFAULT instead?
