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Message-ID: <20161207162618.GP3124@twins.programming.kicks-ass.net>
Date: Wed, 7 Dec 2016 17:26:18 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: David Windsor <dwindsor@...il.com>
Cc: Liljestrand Hans <ishkamiel@...il.com>,
"Reshetova, Elena" <elena.reshetova@...el.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Greg KH <gregkh@...uxfoundation.org>,
Kees Cook <keescook@...omium.org>,
"will.deacon@....com" <will.deacon@....com>,
Boqun Feng <boqun.feng@...il.com>, "aik@...abs.ru" <aik@...abs.ru>,
"david@...son.dropbear.id.au" <david@...son.dropbear.id.au>
Subject: Re: Conversion from atomic_t to refcount_t: summary of issues
On Wed, Dec 07, 2016 at 10:59:47AM -0500, David Windsor wrote:
> On Wed, Dec 7, 2016 at 8:52 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > All in all I'm not inclined to add {add,sub.inc,dec}_return() to
> > refcount, as previously stated, they don't make sense.
>
> Is the plan now to audit all {add,sub,inc,dec}_return() call sites?
> This should probably happen anyway, due to the amount of funkiness
> uncovered by Hans' mini-audit. Then we can rewrite actual reference
> counting code that calls the unsupported {add,sub,inc,dec}_return() to
> use something else?
The ip_vs_dest cache thing would receive 2 patches, one doing the global
+1, the second conversion to refcount_t.
For BPF we'd need to talk to Alexei to see if the custom limit still
makes sense, but I'd be inclined to simply drop that in the refcount_t
conversion.
As to the tty and usb-gadget ones, those constructs are actually racy,
but I'm not sure the races matter. But I would certainly prefer to
rework then to be race-free.
But I wouldn't go so far as to audit all *_return calls, just those that
pop up while hunting refcounts.
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