netdev - Re: UBSAN reports issue in ip_idents

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Message-ID: <1474385116.23058.23.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Tue, 20 Sep 2016 08:25:16 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org
Subject: Re: UBSAN reports issue in ip_idents_reserve

On Tue, 2016-09-20 at 07:11 -0700, Eric Dumazet wrote:
> On Tue, 2016-09-20 at 15:39 +0200, Jiri Pirko wrote:
> 
> > I see. So how to silent the warning?
> > 
> 
> We can replace the atomic_add_return() and use a loop around
> atomic_read() and atomic_cmpxhg()
> 
> This would change the nice property of x86 xadd into a loop.
> 
> Or we also could fallback to random generation if the atomic_cmpxchg()
> fails.
> 
> I'll provide a patch, thanks.
> 

I looks at other places, I am surprised you do not see other UBSAN
issues in networking :)

netdev_refcnt_read() can potentially gives errors as well.