From: "Paul E. McKenney" <paulmck@linux•ibm.com>
To: Peter Zijlstra <peterz@infradead•org>
Cc: "mark.rutland@arm•com" <mark.rutland@arm•com>,
"linux-mips@linux-mips•org" <linux-mips@linux-mips•org>,
"jhogan@kernel•org" <jhogan@kernel•org>,
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"paulus@samba•org" <paulus@samba•org>,
Eric Dumazet <eric.dumazet@gmail•com>,
Trond Myklebust <trondmy@hammerspace•com>,
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"linux@roeck-us•net" <linux@roeck-us•net>,
"arnd@arndb•de" <arnd@arndb•de>,
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Subject: Re: [RFC PATCH] lib: Introduce generic __cmpxchg_u64() and use it where needed
Date: Thu, 1 Nov 2018 13:29:10 -0700 [thread overview]
Message-ID: <20181101202910.GB4170@linux.ibm.com> (raw)
In-Reply-To: <20181101172739.GA3196@hirez.programming.kicks-ass.net>
On Thu, Nov 01, 2018 at 06:27:39PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 01, 2018 at 06:14:32PM +0100, Peter Zijlstra wrote:
> > > This reminds me of this sooooo silly patch :/
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=adb03115f4590baa280ddc440a8eff08a6be0cb7
>
> You'd probably want to write it like so; +- some ordering stuff, that
> code didn't look like it really needs the memory barriers implied by
> these, but I didn't look too hard.
The atomic_fetch_add() API would need to be propagated out to the other
architectures, correct?
Thanx, Paul
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index c0a9d26c06ce..11deb1d7e96b 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -485,16 +485,10 @@ u32 ip_idents_reserve(u32 hash, int segs)
> u32 now = (u32)jiffies;
> u32 new, delta = 0;
>
> - if (old != now && cmpxchg(p_tstamp, old, now) == old)
> + if (old != now && try_cmpxchg(p_tstamp, &old, now))
> delta = prandom_u32_max(now - old);
>
> - /* Do not use atomic_add_return() as it makes UBSAN unhappy */
> - do {
> - old = (u32)atomic_read(p_id);
> - new = old + delta + segs;
> - } while (atomic_cmpxchg(p_id, old, new) != old);
> -
> - return new - segs;
> + return atomic_fetch_add(segs + delta, p_id) + delta;
> }
> EXPORT_SYMBOL(ip_idents_reserve);
>
>
next prev parent reply other threads:[~2018-11-01 20:37 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-31 19:52 [RFC PATCH] lib: Introduce generic __cmpxchg_u64() and use it where needed Guenter Roeck
2018-10-31 21:32 ` Paul Burton
2018-10-31 22:02 ` Guenter Roeck
2018-10-31 23:32 ` Paul Burton
2018-11-01 0:17 ` Trond Myklebust
2018-11-01 13:18 ` Mark Rutland
2018-11-01 14:59 ` Peter Zijlstra
2018-11-01 15:22 ` Trond Myklebust
2018-11-01 16:32 ` Peter Zijlstra
2018-11-01 16:59 ` Eric Dumazet
2018-11-01 17:14 ` Peter Zijlstra
2018-11-01 17:27 ` Peter Zijlstra
2018-11-01 20:29 ` Paul E. McKenney [this message]
2018-11-01 21:38 ` Peter Zijlstra
2018-11-01 22:26 ` Paul E. McKenney
2018-11-01 17:43 ` Paul E. McKenney
2018-11-01 17:01 ` Paul E. McKenney
2018-11-01 17:18 ` Peter Zijlstra
2018-11-01 17:34 ` Paul E. McKenney
2018-11-01 17:46 ` Dmitry Vyukov
2018-11-01 21:45 ` Peter Zijlstra
2018-11-02 10:56 ` David Laight
2018-11-02 12:23 ` Peter Zijlstra
2018-11-02 13:38 ` Paul E. McKenney
2018-11-02 13:37 ` Paul E. McKenney
2018-11-02 16:19 ` Andrey Ryabinin
2018-11-05 10:38 ` Peter Zijlstra
2018-11-05 14:24 ` Peter Zijlstra
2018-11-01 17:54 ` Paul Burton
2018-11-01 1:18 ` Guenter Roeck
2018-11-01 6:30 ` Trond Myklebust
2018-11-01 15:28 ` Guenter Roeck
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