Re: [BUG] arm64: an infinite loop in generic_perform_write()

[Xiaoming Ni]

On 2021/6/23 10:50, Al Viro wrote:
> On Wed, Jun 23, 2021 at 10:39:31AM +0800, Chen Huang wrote:
>
> > Then when kernel handles the alignment_fault, it will not panic. As the
> > arm64 memory model spec said, when the address is not a multiple of the
> > element size, the access is unaligned. Unaligned accesses are allowed to
> > addresses marked as Normal, but not to Device regions. An unaligned access
> > to a Device region will trigger an exception (alignment fault).
> > 	
> > do_alignment_fault
> >      do_bad_area
> > 	__do_kernel_fault
> >             fixup_exception
> >
> > But that fixup cann't handle the unaligned copy, so the
> > copy_page_from_iter_atomic returns 0 and traps in loop.
>
> Looks like you need to fix your raw_copy_from_user(), then...
> .

Exit loop when iov_iter_copy_from_user_atomic() returns 0.
This should solve the problem, too, and it's easier.

Thanks.
Xiaoming Ni