Messages in this thread | | | Date | Mon, 23 Feb 2009 11:59:26 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] mm: fix lazy vmap purging (use-after-free error) |
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On Mon, 23 Feb 2009 11:30:57 -0800 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> On Mon, Feb 23, 2009 at 11:10:09AM -0800, Andrew Morton wrote: > > On Mon, 23 Feb 2009 08:17:26 -0800 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote: > > > > > On Tue, Feb 24, 2009 at 12:29:36AM +1100, Nick Piggin wrote: > > > > On Monday 23 February 2009 16:17:09 Paul E. McKenney wrote: > > > > > > > > > The boot CPU runs in the context of its idle thread during boot-up. > > > > > During this time, idle_cpu(0) will always return nonzero, which will > > > > > fool Classic and Hierarchical RCU into deciding that a large chunk of > > > > > the boot-up sequence is a big long quiescent state. This in turn causes > > > > > RCU to prematurely end grace periods during this time. > > > > > > > > > > This patch creates a new global variable that is set to 1 just before > > > > > the boot CPU first enters the scheduler, after which the idle task > > > > > really is idle. > > > > > > > > Nice work all (btw. if this patch goes in rather than using system_state, > > > > then please make the variable __read_mostly). > > > > > > Hmmm... I misread this and made system_state be __read_mostly. Let > > > me know if this is bad, easy to fix if needed. > > > > Please don't use system_state. The whole thing is just bad design. > > It's a global variable, breaks encapsulation, creates interactions etc. > > CS-101 stuff. > > OK. Would it help if I wrapped an accessor function around system_state?
That doesn't help the core problem: system_state creates interactions between unrelated subsystems. And the number of interactions grows exponentially with the number of subsystems which use system_state.
> I do need some sort of global state if I am to solve this problem. ;-)
As I suggested before, please add a new state variable which is private to your subsystem. That way it remains isolated from other subsystems.
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