Re: [RFC][PATCH] KGDB: remove kgdb-own fault handling (was: Re: [git pull] x86 arch updates for v2.6.25)

Linus Torvalds
2008-02-08T22:00:50Z

On Fri, 8 Feb 2008, Jan Kiszka wrote:
>
> Well, let's try it this way: Find below a patch against kgdb.git that
> removes the special fault handling (this wouldn't be the first feature I
> recently removed from kgdb :->). Light testing revealed no obvious
> problems yet.

That is indeed horrible code. No way will I merge anything that has things
like that even in it's *history* (ie somebody needs to re-generate the
tree without code like that - some things should not be allowed to exist).

That said, while just using "probe_kernel_addr()" is certainly much
better, it's still really inefficient. If you actually want to do a "safe
memory copy", then the right way to do that is basically to do

pagefault_disable();
leftover = __copy_from_user_inatomic(dst, src, count);
pagefault_enable();

if (leftover)
handle_the_fact_that_the_copy_didnt_complete();

which should even be reasonably efficient and should work in all contexts
(hardware interrupts disabled, spinlocks held, you name it).

So all those "kgdb_{get|set}_mem()" things seem bogus (they also have
insane calling semantics - return NULL or errptr? Why not just return an
integer error code?

Linus