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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 15 Jun 2020 11:07:29 -0700
Message-ID: <CAKwvOd=shEiDQZxZPyUCC=CJLrzmP5FHr04cE-KVN_-6+qz1jQ@mail.gmail.com>
Subject: Re: net/sched/sch_fq.c:966:12: warning: stack frame size of 1400
 bytes in function 'fq_dump'
To:     Eric Dumazet <edumazet@google.com>
Cc:     kernel test robot <lkp@intel.com>, kbuild-all@lists.01.org,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, Jun 15, 2020 at 10:59 AM 'Eric Dumazet' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:
>
> On Mon, Jun 15, 2020 at 10:54 AM Eric Dumazet <edumazet@google.com> wrote:
> >
> > On Mon, Jun 15, 2020 at 10:44 AM Nick Desaulniers
> > <ndesaulniers@google.com> wrote:
> > >
> > > On Mon, Jun 15, 2020 at 9:17 AM 'Eric Dumazet' via Clang Built Linux
> > > <clang-built-linux@googlegroups.com> wrote:
> > > >
> > > > On Sun, Jun 14, 2020 at 11:26 PM kernel test robot <lkp@intel.com> wrote:
> > > > >
> > > > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > > > head:   96144c58abe7ff767e754b5b80995f7b8846d49b
> > > > > commit: 39d010504e6b4485d7ceee167743620dd33f4417 net_sched: sch_fq: add horizon attribute
> > > > > date:   6 weeks ago
> > > > > :::::: branch date: 3 hours ago
> > > > > :::::: commit date: 6 weeks ago
> > > > > config: arm-randconfig-r006-20200614 (attached as .config)
> > > > > compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project c669a1ed6386d57a75a602b53266466dae1e1d84)
> > > > > reproduce (this is a W=1 build):
> > > > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > > > >         chmod +x ~/bin/make.cross
> > > > >         # install arm cross compiling tool for clang build
> > > > >         # apt-get install binutils-arm-linux-gnueabi
> > > > >         git checkout 39d010504e6b4485d7ceee167743620dd33f4417
> > > > >         # save the attached .config to linux build tree
> > > > >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm
> > > > >
> > > > > If you fix the issue, kindly add following tag as appropriate
> > > > > Reported-by: kernel test robot <lkp@intel.com>
> > > > >
> > > > > All warnings (new ones prefixed by >>, old ones prefixed by <<):
> > > > >
> > > > > >> net/sched/sch_fq.c:966:12: warning: stack frame size of 1400 bytes in function 'fq_dump' [-Wframe-larger-than=]
> > > > > static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
> > > > > ^
> > > >
> > > >
> > > > This looks like a bug in CLANG on ARM, there is no way fq_dump() could
> > > > consume so much stack space.
> > >
> > > You can use
> > > https://github.com/ClangBuiltLinux/frame-larger-than
> > > to help debug these.  You might be surprised who's doing larger stack
> > > allocations than expected.
> >
> > What is wrong with scripts/checkstack.pl  ?
>
> After using CLANG on x86 I get :
>
> $ objdump -d net/sched/sch_fq.o | scripts/checkstack.pl
> 0x00001136 fq_change [sch_fq.o]: 192
> 0x00000016 __direct_call_Qdisc_enqueue1 [sch_fq.o]: 112
> 0x000019e0 fq_dump_stats [sch_fq.o]: 112
> 0x00001b43 fq_dump_stats [sch_fq.o]: 112
>
> So CLANG on x86 seems fine.
>
> I said : " this looks like a bug in CLANG on ARM"

This is a randconfig, so some option is turning on something that's
causing excessive stack usage with your patch on ARM.  Building who
knows what config with x86 and claiming it works doesn't really cut
it.  You looked at fq_dump and claimed it should be fine.  Did you
verify each called function that was inlined?

And the issue with checkstack is it tells you the depth, but not *what
variables* and from which inlined function may be the cause.

>
>
>
> >
> > >
> > > >
> > > >
> > > >
> > > > > 1 warning generated.
> > > > >
> > > > > # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=39d010504e6b4485d7ceee167743620dd33f4417
> > > > > git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > > > > git remote update linus
> > > > > git checkout 39d010504e6b4485d7ceee167743620dd33f4417
> > > > > vim +/fq_dump +966 net/sched/sch_fq.c
> > > > >
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   965
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29  @966  static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   967  {
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   968          struct fq_sched_data *q = qdisc_priv(sch);
> > > > > 48872c11b77271 Eric Dumazet   2018-11-11   969          u64 ce_threshold = q->ce_threshold;
> > > > > 39d010504e6b44 Eric Dumazet   2020-05-01   970          u64 horizon = q->horizon;
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   971          struct nlattr *opts;
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   972
> > > > > ae0be8de9a53cd Michal Kubecek 2019-04-26   973          opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   974          if (opts == NULL)
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   975                  goto nla_put_failure;
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   976
> > > > > 65c5189a2b57b9 Eric Dumazet   2013-11-15   977          /* TCA_FQ_FLOW_DEFAULT_RATE is not used anymore */
> > > > > 65c5189a2b57b9 Eric Dumazet   2013-11-15   978
> > > > > 48872c11b77271 Eric Dumazet   2018-11-11   979          do_div(ce_threshold, NSEC_PER_USEC);
> > > > > 39d010504e6b44 Eric Dumazet   2020-05-01   980          do_div(horizon, NSEC_PER_USEC);
> > > > > 48872c11b77271 Eric Dumazet   2018-11-11   981
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   982          if (nla_put_u32(skb, TCA_FQ_PLIMIT, sch->limit) ||
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   983              nla_put_u32(skb, TCA_FQ_FLOW_PLIMIT, q->flow_plimit) ||
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   984              nla_put_u32(skb, TCA_FQ_QUANTUM, q->quantum) ||
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   985              nla_put_u32(skb, TCA_FQ_INITIAL_QUANTUM, q->initial_quantum) ||
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   986              nla_put_u32(skb, TCA_FQ_RATE_ENABLE, q->rate_enable) ||
> > > > > 76a9ebe811fb3d Eric Dumazet   2018-10-15   987              nla_put_u32(skb, TCA_FQ_FLOW_MAX_RATE,
> > > > > 76a9ebe811fb3d Eric Dumazet   2018-10-15   988                          min_t(unsigned long, q->flow_max_rate, ~0U)) ||
> > > > > f52ed89971adbe Eric Dumazet   2013-11-15   989              nla_put_u32(skb, TCA_FQ_FLOW_REFILL_DELAY,
> > > > > f52ed89971adbe Eric Dumazet   2013-11-15   990                          jiffies_to_usecs(q->flow_refill_delay)) ||
> > > > > 06eb395fa9856b Eric Dumazet   2015-02-04   991              nla_put_u32(skb, TCA_FQ_ORPHAN_MASK, q->orphan_mask) ||
> > > > > 77879147a3481b Eric Dumazet   2016-09-19   992              nla_put_u32(skb, TCA_FQ_LOW_RATE_THRESHOLD,
> > > > > 77879147a3481b Eric Dumazet   2016-09-19   993                          q->low_rate_threshold) ||
> > > > > 48872c11b77271 Eric Dumazet   2018-11-11   994              nla_put_u32(skb, TCA_FQ_CE_THRESHOLD, (u32)ce_threshold) ||
> > > > > 583396f4ca4d6e Eric Dumazet   2020-03-16   995              nla_put_u32(skb, TCA_FQ_BUCKETS_LOG, q->fq_trees_log) ||
> > > > > 39d010504e6b44 Eric Dumazet   2020-05-01   996              nla_put_u32(skb, TCA_FQ_TIMER_SLACK, q->timer_slack) ||
> > > > > 39d010504e6b44 Eric Dumazet   2020-05-01   997              nla_put_u32(skb, TCA_FQ_HORIZON, (u32)horizon) ||
> > > > > 39d010504e6b44 Eric Dumazet   2020-05-01   998              nla_put_u8(skb, TCA_FQ_HORIZON_DROP, q->horizon_drop))
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29   999                  goto nla_put_failure;
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29  1000
> > > > > d59b7d8059ddc4 Yang Yingliang 2014-03-12  1001          return nla_nest_end(skb, opts);
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29  1002
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29  1003  nla_put_failure:
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29  1004          return -1;
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29  1005  }
> > > > > afe4fd062416b1 Eric Dumazet   2013-08-29  1006
> > > > >
> > > > > :::::: The code at line 966 was first introduced by commit
> > > > > :::::: afe4fd062416b158a8a8538b23adc1930a9b88dc pkt_sched: fq: Fair Queue packet scheduler
> > > > >
> > > > > :::::: TO: Eric Dumazet <edumazet@google.com>
> > > > > :::::: CC: David S. Miller <davem@davemloft.net>
> > > > >
> > > > > ---
> > > > > 0-DAY CI Kernel Test Service, Intel Corporation
> > > > > https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
> > > > > _______________________________________________
> > > > > kbuild mailing list -- kbuild@lists.01.org
> > > > > To unsubscribe send an email to kbuild-leave@lists.01.org
> > > >
> > > > --
> > > > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
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> > >
> > >
> > >
> > > --
> > > Thanks,
> > > ~Nick Desaulniers
>
> --
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-- 
Thanks,
~Nick Desaulniers