Re: [PATCH 2/5] coredump: Fix handling of partial writes in dump_emit()

[Jann Horn]

On Tue, Apr 28, 2020 at 5:36 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Apr 27, 2020 at 8:28 PM Jann Horn <jannh@xxxxxxxxxx> wrote:
> >
> > After a partial write, we have to update the input buffer pointer.
>
> Interesting. It seems this partial write case never triggers (except
> for actually killing the core-dump).
>
> Or did you find a case where it actually matters?
>
> Your fix is obviously correct, but it also makes me go "that function
> clearly never actually worked for partial writes, maybe we shouldn't
> even bother?"

Hmm, yeah... I can't really think of cases where write handlers can
spuriously return early without having a pending signal, and a second
write is likely to succeed... I just know that there are some things
that are notorious for returning short *reads* (e.g. pipes, sockets,
/proc/$pid/maps).

Al's commit message refers to pipes specifically; but even at commit
2507a4fbd48a, I don't actually see where pipe_write() could return a
short write without a page allocation failure or something like that.

So maybe you're right and we should just get rid of it...