Re: [RFC PATCH 2/5] powerpc: Exception hooks for context tracking subsystem

[Li Zhong <zhong@linux.vnet.ibm.com>]

On Sun, 2013-02-10 at 15:10 +0100, Frederic Weisbecker wrote:
> 2013/2/1 Li Zhong <zhong@linux.vnet.ibm.com>:
> > This is the exception hooks for context tracking subsystem, including
> > data access, program check, single step, instruction breakpoint, machine check,
> > alignment, fp unavailable, altivec assist, unknown exception, whose handlers
> > might use RCU.
> >
> > This patch corresponds to
> > [PATCH] x86: Exception hooks for userspace RCU extended QS
> >   commit 6ba3c97a38803883c2eee489505796cb0a727122
> >
> > Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
> 
> Looks good!
> 
> I guess we should move exception_enter/exit definition to the generic
> code. They should be the same for all archs after all. 

Indeed.

> Also we are
> relying on user_mode(regs) but this may be buggy with some corner
> cases. For example if an exception happen after a call to user_exit()

I guess you mean user_enter() here, or am I confused?

> (on syscall exit) but before we actually resume in userspace, the
> exception will exit in kernel mode from the context tracking POV.
> 
> So instead on relying on the regs, which are not sync with the context
> tracking state, we should use something like:
> 
> prev_state = exception_enter();
> ...
> exception_exit(prev_state);
> 
> Also preempt_schedule_irq() is concerned as well by this problem. So I
> should convert it to that scheme as well. I'm going to prepare some
> patches.
> 
> Feel free to merge this patch in the powerpc tree, I'll do the
> conversion along the way.

Or if your patches gets merged earlier than these, I can update my code
according to yours.

Thanks, Zhong

> 
> Thanks.
>