Re: Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"?

[Linus Torvalds]

On Tue, Jun 22, 2021 at 11:23 AM David Howells <dhowells@xxxxxxxxxx> wrote:
>
> Probably the most obvious way would be to set a flag in task_struct saying
> what you're doing and have the point that would otherwise wait for the page to
> become unlocked skip to the fault fixup code if the page is locked after
> ->readahead() has been invoked and the flag is set, then use get_user() in
> iov_iter_fault_in_readable().

Yeah, the existing user access exception handling code _almost_
handles it, except for one thing: you'd need to have some way to
distinguish between "prefetch successful" and "fault failed".

And yeah, I guess it could be a flag in task_struct, but at that point
my gag reflex starts acting up.

               Linus