From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu,
John Stultz <john.stultz@linaro.org>,
"David S. Miller" <davem@davemloft.net>,
Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Eric Dumazet <eric.dumazet@gmail.com>,
Kevin Easton <kevin@guarana.org>
Subject: Re: [PATCH tip/core/rcu 11/11] jiffies: Avoid undefined behavior from signed overflow
Date: Sun, 18 Aug 2013 17:41:20 -0700 [thread overview]
Message-ID: <20130819004120.GU29406@linux.vnet.ibm.com> (raw)
In-Reply-To: <20130818032350.GO28923@leaf>
On Sat, Aug 17, 2013 at 08:23:51PM -0700, Josh Triplett wrote:
> On Sat, Aug 17, 2013 at 06:37:56PM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> >
> > According to the C standard 3.4.3p3, overflow of a signed integer results
> > in undefined behavior. This commit therefore changes the definitions
> > of time_after(), time_after_eq(), time_after64(), and time_after_eq64()
> > to avoid this undefined behavior. The trick is that the subtraction
> > is done using unsigned arithmetic, which according to 6.2.5p9 cannot
> > overflow because it is defined as modulo arithmetic. This has the added
> > (though admittedly quite small) benefit of shortening two lines of code
> > by four characters each.
> >
> > Note that the C standard considers the cast from unsigned to
> > signed to be implementation-defined, see 6.3.1.3p3. However, on a
> > two-complement system, an implementation that defines anything other
> > than a reinterpretation of the bits is free come to me, and I will be
>
> s/free come/free to come/
Good catch, fixed!
Thanx, Paul
> > happy to act as a witness for its being committed to an insane asylum.
>
> With the typo above fixed:
> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
>
next prev parent reply other threads:[~2013-08-19 0:41 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-18 1:37 [PATCH tip/core/rcu 0/11] Fixes for 3.12 Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 01/11] rcu: Expedite grace periods during suspend/resume Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 02/11] rcu: Expedite during suspend and resume only on smallish systems Paul E. McKenney
2013-08-18 3:18 ` Josh Triplett
2013-08-19 0:32 ` Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 03/11] rcu: Simplify debug-objects fixups Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 04/11] debugobjects: Make debug_object_activate() return status Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 05/11] rcu: Make call_rcu() leak callbacks for debug-object errors Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 06/11] rcu: Switch to exedited grace periods for suspend as well as hibernation Paul E. McKenney
2013-08-18 3:20 ` Josh Triplett
2013-08-19 0:33 ` Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 07/11] rcu: Avoid redundant grace-period kthread wakeups Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 08/11] rculist: list_first_or_null_rcu() should use list_entry_rcu() Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 09/11] rcu: Select IRQ_WORK from TREE_PREEMPT_RCU Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 10/11] rcu: Simplify _rcu_barrier() processing Paul E. McKenney
2013-08-18 1:37 ` [PATCH tip/core/rcu 11/11] jiffies: Avoid undefined behavior from signed overflow Paul E. McKenney
2013-08-18 3:23 ` Josh Triplett
2013-08-19 0:41 ` Paul E. McKenney [this message]
2013-08-19 1:20 ` Josh Triplett
2013-08-19 4:14 ` Paul E. McKenney
2013-08-18 3:17 ` [PATCH tip/core/rcu 01/11] rcu: Expedite grace periods during suspend/resume Josh Triplett
2013-08-18 9:34 ` Borislav Petkov
2013-08-19 0:29 ` Paul E. McKenney
2013-08-19 9:18 ` Borislav Petkov
2013-08-18 3:24 ` [PATCH tip/core/rcu 0/11] Fixes for 3.12 Josh Triplett
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