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

From: Nathan Chancellor
Date: Tue Jun 08 2021 - 11:53:45 EST


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@xxxxxxxxx>

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@xxxxxxxxxx>
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@xxxxxxxxx>
Tested-by: Rong Chen <rong.a.chen@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

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).

{
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 void rcu_gp_fqs_loop(void)
{
bool first_gp_fqs;
int gf = 0;


Cheers,
Nathan