Messages in this thread | | | Date | Fri, 4 Jul 2003 12:21:23 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH 2.5.73] Signal stack fixes #1 introduce PF_SS_ACTIVE |
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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
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