lkml.org 
[lkml]   [2003]   [Jul]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2.5.73] Signal stack fixes #1 introduce PF_SS_ACTIVE

On Fri, 4 Jul 2003, Jörn Engel wrote:
>
> This is the generic part of the signal stack fixes, it simply
> introduces a new PF-flag that indicates whether we are using the
> signal stack right now or not.

My reason for disliking this patch is that it adds user-space information
to the kernel - in a place where user space cannot get at it.

In particular, any traditional cooperative user-space threading package
wants to switch its own stack around, and they all do it by just changing
%esp directly. The whole point of such threading is that it's _fast_,
since it doesn't need any kernel support (and since it's cooperative, you
can avoid locking).

The old "optimization" that you didn't like was not an optimization at
all: it got the case of user space changing stacks _right_, while still
allowing yet another stack for signal handling and exiting the signal by
hand.

Does anybody do that? I don't know. But it was done the way it was done on
purpose.

Linus

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2009-11-18 23:46    [from the cache]
©2003-2011 Jasper Spaans