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Subject: Re: [kbuild-all] Re: kernel/rcu/tree.c:2073:23: warning: stack frame
 size of 2704 bytes in function 'rcu_gp_kthread'
To:     paulmck@kernel.org
Cc:     Rong Chen <rong.a.chen@intel.com>,
        kernel test robot <lkp@intel.com>, kbuild-all@lists.01.org,
        clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org
References: <202106061253.0X2QKyyI-lkp@intel.com>
 <20210606044926.GJ4397@paulmck-ThinkPad-P17-Gen-1>
 <4696fe3d-a7ad-acae-686e-6295ca327737@intel.com>
 <20210607151939.GP4397@paulmck-ThinkPad-P17-Gen-1>
 <e7bbb0e5-3063-031b-af6e-273e97f1d61f@intel.com>
 <20210608050134.GZ4397@paulmck-ThinkPad-P17-Gen-1>
 <f3cc5211-0c68-17c8-a222-4bc2c2525522@kernel.org>
 <20210609035805.GA4397@paulmck-ThinkPad-P17-Gen-1>
From:   Nathan Chancellor <nathan@kernel.org>
Message-ID: <7f03e5bc-d8a3-74a4-273a-f8047b62ab02@kernel.org>
Date:   Tue, 8 Jun 2021 21:14:29 -0700
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On 6/8/2021 8:58 PM, Paul E. McKenney wrote:
> On Tue, Jun 08, 2021 at 08:53:17AM -0700, Nathan Chancellor wrote:
>> On 6/7/2021 10:01 PM, Paul E. McKenney wrote:
>>> On Tue, Jun 08, 2021 at 11:14:40AM +0800, Rong Chen wrote:
>>>>
>>>>
>>>> On 6/7/21 11:19 PM, Paul E. McKenney wrote:
>>>>> On Mon, Jun 07, 2021 at 05:18:21PM +0800, Rong Chen wrote:
>>>>>>
>>>>>> On 6/6/21 12:49 PM, Paul E. McKenney wrote:
>>>>>>> On Sun, Jun 06, 2021 at 12:19:57PM +0800, kernel test robot wrote:
>>>>>>>> Hi Paul,
>>>>>>>>
>>>>>>>> FYI, the error/warning still remains.
>>>>>>>>
>>>>>>>> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>>>>>>>> head:   f5b6eb1e018203913dfefcf6fa988649ad11ad6e
>>>>>>>> commit: 7dffe01765d9309b8bd5505503933ec0ec53d192 rcu: Add lockdep_assert_irqs_disabled() to raw_spin_unlock_rcu_node() macros
>>>>>>>> date:   5 months ago
>>>>>>>> config: powerpc-randconfig-r023-20210606 (attached as .config)
>>>>>>>> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 551a697c5cf33275b66add4fc467fcf59084cffb)
>>>>>>>> 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 powerpc cross compiling tool for clang build
>>>>>>>>             # apt-get install binutils-powerpc-linux-gnu
>>>>>>>>             # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7dffe01765d9309b8bd5505503933ec0ec53d192
>>>>>>>>             git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>>>>>>>>             git fetch --no-tags linus master
>>>>>>>>             git checkout 7dffe01765d9309b8bd5505503933ec0ec53d192
>>>>>>>>             # save the attached .config to linux build tree
>>>>>>>>             COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=powerpc
>>>>>>>>
>>>>>>>> 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 >>):
>>>>>>>>
>>>>>>>>        In file included from kernel/rcu/tree.c:21:
>>>>>>>>        In file included from include/linux/kernel.h:12:
>>>>>>>>        In file included from include/linux/bitops.h:29:
>>>>>>>>        In file included from arch/powerpc/include/asm/bitops.h:62:
>>>>>>>>        arch/powerpc/include/asm/barrier.h:49:9: warning: '__lwsync' macro redefined [-Wmacro-redefined]
>>>>>>>>        #define __lwsync()      __asm__ __volatile__ (stringify_in_c(LWSYNC) : : :"memory")
>>>>>>>>                ^
>>>>>>>>        <built-in>:310:9: note: previous definition is here
>>>>>>>>        #define __lwsync __builtin_ppc_lwsync
>>>>>>>>                ^
>>>>>>>>>> kernel/rcu/tree.c:2073:23: warning: stack frame size of 2704 bytes in function 'rcu_gp_kthread' [-Wframe-larger-than=]
>>>>>>>>        static int __noreturn rcu_gp_kthread(void *unused)
>>>>>>> Does -rcu commit 2f20de99a63b ("rcu: Make rcu_gp_cleanup() be noinline
>>>>>>> for tracing") help?
>>>>>> Hi Paul,
>>>>>>
>>>>>> The stack frame size decreased to 2256 bytes:
>>>>>>
>>>>>>      kernel/rcu/tree.c:2129:23: warning: stack frame size of 2256 bytes in
>>>>>> function 'rcu_gp_kthread' [-Wframe-larger-than=]
>>>>> Very good, thank you!  Does the following patch (in addition to that
>>>>> commit) also help?
>>>>
>>>> Hi Paul,
>>>>
>>>> I applied the below patch on commit 2f20de99a63b and the warning is gone.
>>>
>>> Very good, and thank you for your testing.  I have applied the requested
>>> Reported-by and your Tested-by on the commit shown below.  Please let
>>> me know if you would prefer some other Reported/Tested setup.
>>>
>>> 							Thanx, Paul
>>>
>>> ------------------------------------------------------------------------
>>>
>>> commit 336e92638287615d47c07af4ff6feb397cfe2084
>>> Author: Paul E. McKenney <paulmck@kernel.org>
>>> Date:   Mon Jun 7 21:57:02 2021 -0700
>>>
>>>       rcu: Make rcu_gp_init() and rcu_gp_fqs_loop noinline to conserve stack
>>>       The kbuild test project found an oversized stack frame in rcu_gp_kthread()
>>>       for some kernel configurations.  This oversizing was due to a very large
>>>       amount of inlining, which is unnecessary due to the fact that this code
>>>       executes infrequently.  This commit therefore marks rcu_gp_init() and
>>>       rcu_gp_fqs_loop noinline to conserve stack space.
>>>       Reported-by: kernel test robot <lkp@intel.com>
>>>       Tested-by: Rong Chen <rong.a.chen@intel.com>
>>>       Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>>>
>>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>>> index 13bd8eee62bf..ef435aeac993 100644
>>> --- a/kernel/rcu/tree.c
>>> +++ b/kernel/rcu/tree.c
>>> @@ -1737,7 +1737,7 @@ static void rcu_strict_gp_boundary(void *unused)
>>>    /*
>>>     * Initialize a new grace period.  Return false if no grace period required.
>>>     */
>>> -static bool rcu_gp_init(void)
>>> +static noinline bool rcu_gp_init(void)
>>
>> Small comment if it is not too late. noinline_for_stack expands to the same
>> thing but is self documenting :) that way people do not have to git blame to
>> see why these are marked as noinline (not that too many people are probably
>> touching this but still).
> 
> How about like the following?
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit 8aa0ceef4264012abd7b98d29f0a968f0f0046cb
> Author: Paul E. McKenney <paulmck@kernel.org>
> Date:   Mon Jun 7 21:57:02 2021 -0700
> 
>      rcu: Make rcu_gp_init() and rcu_gp_fqs_loop noinline to conserve stack
>      
>      The kbuild test project found an oversized stack frame in rcu_gp_kthread()
>      for some kernel configurations.  This oversizing was due to a very large
>      amount of inlining, which is unnecessary due to the fact that this code
>      executes infrequently.  This commit therefore marks rcu_gp_init() and
>      rcu_gp_fqs_loop noinline_for_stack to conserve stack space.
>      
>      Reported-by: kernel test robot <lkp@intel.com>
>      Tested-by: Rong Chen <rong.a.chen@intel.com>
>      [ paulmck: noinline_for_stack per Nathan Chancellor. ]
>      Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

Thanks!

> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 13bd8eee62bf..d8052adcdcb1 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1737,7 +1737,7 @@ static void rcu_strict_gp_boundary(void *unused)
>   /*
>    * Initialize a new grace period.  Return false if no grace period required.
>    */
> -static bool rcu_gp_init(void)
> +static noinline_for_stack bool rcu_gp_init(void)
>   {
>   	unsigned long firstseq;
>   	unsigned long flags;
> @@ -1931,7 +1931,7 @@ static void rcu_gp_fqs(bool first_time)
>   /*
>    * Loop doing repeated quiescent-state forcing until the grace period ends.
>    */
> -static void rcu_gp_fqs_loop(void)
> +static noinline_for_stack void rcu_gp_fqs_loop(void)
>   {
>   	bool first_gp_fqs;
>   	int gf = 0;
>