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Date: Fri, 17 Jan 2020 13:32:53 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Shaokun Zhang <zhangshaokun@...ilicon.com> Cc: Eric Dumazet <eric.dumazet@...il.com>, David Miller <davem@...emloft.net>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, jinyuqi@...wei.com, kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org, edumazet@...gle.com, guoyang2@...wei.com, Will Deacon <will@...nel.org> Subject: Re: [PATCH] net: optimize cmpxchg in ip_idents_reserve On Fri, Jan 17, 2020 at 02:54:03PM +0800, Shaokun Zhang wrote: > So how about this? ;-) > > delta = prandom_u32_max(now - old); > > +#ifdef CONFIG_UBSAN > /* Do not use atomic_add_return() as it makes UBSAN unhappy */ > + old = (u32)atomic_read(p_id); > do { > - old = (u32)atomic_read(p_id); > new = old + delta + segs; > - } while (atomic_cmpxchg(p_id, old, new) != old); > + } while (!atomic_try_cmpxchg(p_id, &old, new)); > +#else > + new = atomic_add_return(segs + delta, p_id); > +#endif That's crazy, just accept that UBSAN is taking bonghits and ignore it. Use atomic_add_return() unconditionally.
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