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[204.195.112.199]) by smtp.gmail.com with ESMTPSA id u15-20020a170902714f00b00168c1668a49sm2334325plm.85.2022.06.16.20.08.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Jun 2022 20:08:16 -0700 (PDT) Date: Thu, 16 Jun 2022 20:08:14 -0700 From: Stephen Hemminger To: Peilin Ye Cc: Jamal Hadi Salim , Cong Wang , Jiri Pirko , Peilin Ye , Yuming Chen , Ted Lin , Dave Taht , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Cong Wang Subject: Re: [PATCH net] net/sched: sch_netem: Fix arithmetic in netem_dump() for 32-bit platforms Message-ID: <20220616200814.15fff125@hermes.local> In-Reply-To: <20220616234336.2443-1-yepeilin.cs@gmail.com> References: <20220616234336.2443-1-yepeilin.cs@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 16 Jun 2022 16:43:36 -0700 Peilin Ye wrote: > From: Peilin Ye > > As reported by Yuming, currently tc always show a latency of UINT_MAX > for netem Qdisc's on 32-bit platforms: > > $ tc qdisc add dev dummy0 root netem latency 100ms > $ tc qdisc show dev dummy0 > qdisc netem 8001: root refcnt 2 limit 1000 delay 275s 275s > ^^^^^^^^^^^^^^^^ > > Let us take a closer look at netem_dump(): > > qopt.latency = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->latency, > UINT_MAX); > > qopt.latency is __u32, psched_tdiff_t is signed long, > (psched_tdiff_t)(UINT_MAX) is negative for 32-bit platforms, so > qopt.latency is always UINT_MAX. > > Fix it by using psched_time_t (u64) instead. > > Note: confusingly, users have two ways to specify 'latency': > > 1. normally, via '__u32 latency' in struct tc_netem_qopt; > 2. via the TCA_NETEM_LATENCY64 attribute, which is s64. > > For the second case, theoretically 'latency' could be negative. This > patch ignores that corner case, since it is broken (i.e. assigning a > negative s64 to __u32) anyways, and should be handled separately. > > Thanks Ted Lin for the analysis [1] . > > [1] https://github.com/raspberrypi/linux/issues/3512 > > Reported-by: Yuming Chen > Fixes: 112f9cb65643 ("netem: convert to qdisc_watchdog_schedule_ns") > Reviewed-by: Cong Wang > Signed-off-by: Peilin Ye > --- > net/sched/sch_netem.c | 4 ++-- Thanks for fixing. Guess it is time to run netem on one of the Pi's. Acked-by: Stephen Hemminger