linux-kernel - Re: [kbuild-all] Re: kernel/rcu/tree.c:2073:23: warning: stack frame size of 2704 bytes in function 'rcu_gp

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Date:   Wed, 9 Jun 2021 10:23:09 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Rong Chen <rong.a.chen@...el.com>,
        kernel test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [kbuild-all] Re: kernel/rcu/tree.c:2073:23: warning: stack frame
 size of 2704 bytes in function 'rcu_gp_kthread'

On Tue, Jun 08, 2021 at 09:14:29PM -0700, Nathan Chancellor wrote:
> 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@...el.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@...nel.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@...el.com>
> > > >       Tested-by: Rong Chen <rong.a.chen@...el.com>
> > > >       Signed-off-by: Paul E. McKenney <paulmck@...nel.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@...nel.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@...el.com>
> >      Tested-by: Rong Chen <rong.a.chen@...el.com>
> >      [ paulmck: noinline_for_stack per Nathan Chancellor. ]
> >      Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> 
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>

Applied, thank you!

							Thanx, Paul

> 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;
> >