[PATCH -tip 2/2] [BUGFIX] kprobes/x86: Fix removed int3 checking order

[Ananth N Mavinakayanahalli]

On Tue, Apr 27, 2010 at 06:33:49PM -0400, Masami Hiramatsu wrote:
> Fix kprobe/x86 to check removed int3 when failing to get kprobe
> from hlist. Since we have a time window between checking int3
> exists on probed address and getting kprobe on that address,
> we can have following senario.
> -------
> CPU1                     CPU2
> hit int3
> check int3 exists
>                          remove int3
>                          remove kprobe from hlist
> get kprobe from hlist
> no kprobe->OOPS!
> -------

Do you have a testcase for this issue?

> This patch moves int3 checking if there is no kprobe on that
> address for fixing this problem as follows;
> ------
> CPU1                     CPU2
> hit int3
>                          remove int3
>                          remove kprobe from hlist
> get kprobe from hlist
> no kprobe->check int3 exists
>          ->rollback&retry
> ------

You may also want to fix up the comment on top of kprobe_handler() about
the interrupt gate as its only true for x86_32 and not x86_64, right?

> Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> Cc: Dave Anderson <anderson@redhat.com>
> Cc: Ingo Molnar <mingo@elte.hu>

Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>