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

[Al Viro]

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...