Re: [PATCH 4/5] x86: Allow nesting of the debug stack IDT setting

["H. Peter Anvin" <hpa@zytor.com>]

On 05/30/2012 06:28 PM, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
> 
> When the NMI handler runs, it checks if it preempted a debug
> handler and if that handler is using the debug stack. If it is, it
> changes the IDT table not to update the stack, otherwise it will
> reset the debug stack and corrupt the debug handler it preempted.
> 
> Now that ftrace uses breakpoints to change functions from nops to 
> callers, many more places may hit a breakpoint. Unfortunately this 
> includes some of the calls that lockdep performs. Which causes
> issues with the debug stack. It too needs to change the debug stack
> before tracing (if called from the debug handler).
> 
> Allow the debug_stack_set_zero() and debug_stack_reset() to be
> nested so that the debug handlers can take advantage of them too.
> 

NAK on this in its current form.  A few minutes to let me write up a
technical review.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.