linux-kernel - Re: [PATCH] mm: fix lazy vmap purging (use-after-free error)

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Date:	Mon, 23 Feb 2009 21:09:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	paulmck@...ux.vnet.ibm.com, nickpiggin@...oo.com.au,
	vegard.nossum@...il.com, stable@...nel.org, npiggin@...e.de,
	penberg@...helsinki.fi, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: fix lazy vmap purging (use-after-free error)


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Mon, 23 Feb 2009 20:33:51 +0100
> Ingo Molnar <mingo@...e.hu> wrote:
> 
> > > > > 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, i've removed the patch
> 
> Thanks.
> 
> > - Paul, would you mind to re-send your original flag 
> > solution, with it marked __read_mostly and with the extern 
> > declarations put into a suitable header file?
> 
> It would still make sense to mark system_state __read_mostly.
> 
> (That's assuming that __read_mostly makes sense.  I still 
> wanna rename it to 
> __pack_all_write_often_variables_into_the_same_cacheline and 
> see what happens then)

the write often variables should be on separate cachelines. 
Putting them on the same cacheline as a read-mostly variable is 
not helpful.

	Ingo
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