linux-kernel - Re: [PATCH 4.19 088/323] locking/lockdep: Avoid RCU-induced noinstr fail

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Date:   Sun, 28 Nov 2021 13:11:11 +0100
From:   Salvatore Bonaccorso <carnil@...ian.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 088/323] locking/lockdep: Avoid RCU-induced noinstr
 fail

Hi,

On Sun, Nov 28, 2021 at 12:59:24PM +0100, Salvatore Bonaccorso wrote:
> Hi,
> 
> On Sun, Nov 28, 2021 at 10:46:13AM +0100, Salvatore Bonaccorso wrote:
> > Hi,
> > 
> > On Wed, Nov 24, 2021 at 12:54:38PM +0100, Greg Kroah-Hartman wrote:
> > > From: Peter Zijlstra <peterz@...radead.org>
> > > 
> > > [ Upstream commit ce0b9c805dd66d5e49fd53ec5415ae398f4c56e6 ]
> > > 
> > > vmlinux.o: warning: objtool: look_up_lock_class()+0xc7: call to rcu_read_lock_any_held() leaves .noinstr.text section
> > 
> > For 4.19.218 at least this commit seems to cause a build failure for
> > cpupower, if warnings are treated as errors, I have not seen the same
> > for the 5.10.80 build:
> > 
> > gcc -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -DVERSION=\"4.19\" -DPACKAGE=\"cpupower\" -DPACKAGE_BUGREPORT=\"Debian\ \(reportbug\ linux-cpupower\)\" -D_GNU_SOURCE -pipe -DNLS -Wall -Wchar-subscripts -Wpointer-arith
> >  -Wsign-compare -Wno-pointer-sign -Wdeclaration-after-statement -Wshadow -Os -fomit-frame-pointer -fPIC -o /home/build/linux-4.19.218/debian/build/build-tools/tools/power/cpupower/lib/cpupower.o -c lib/cpupower.c
> > In file included from lockdep.c:28:
> > ../../../kernel/locking/lockdep.c: In function ‘look_up_lock_class’:
> > ../../../kernel/locking/lockdep.c:694:2: error: implicit declaration of function ‘hlist_for_each_entry_rcu_notrace’; did you mean ‘hlist_for_each_entry_continue’? [-Werror=implicit-function-declaration]
> >   hlist_for_each_entry_rcu_notrace(class, hash_head, hash_entry) {
> >   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >   hlist_for_each_entry_continue
> > ../../../kernel/locking/lockdep.c:694:53: error: ‘hash_entry’ undeclared (first use in this function); did you mean ‘hash_ptr’?
> >   hlist_for_each_entry_rcu_notrace(class, hash_head, hash_entry) {
> >                                                      ^~~~~~~~~~
> >                                                      hash_ptr
> > ../../../kernel/locking/lockdep.c:694:53: note: each undeclared identifier is reported only once for each function it appears in
> > ../../../kernel/locking/lockdep.c:694:64: error: expected ‘;’ before ‘{’ token
> >   hlist_for_each_entry_rcu_notrace(class, hash_head, hash_entry) {
> >                                                                 ^~
> >                                                                 ;
> > ../../../kernel/locking/lockdep.c:706:1: warning: control reaches end of non-void function [-Wreturn-type]
> >  }
> >  ^
> > cc1: some warnings being treated as errors
> > make[5]: *** [/home/build/linux-4.19.218/tools/build/Makefile.build:97: /home/build/linux-4.19.218/debian/build/build-tools/tools/lib/lockdep/lockdep.o] Error 1
> > make[4]: *** [Makefile:121: /home/build/linux-4.19.218/debian/build/build-tools/tools/lib/lockdep/liblockdep-in.o] Error 2
> > make[4]: Leaving directory '/home/build/linux-4.19.218/tools/lib/lockdep'
> > make[3]: *** [/home/build/linux-4.19.218/debian/rules.d/tools/lib/lockdep/Makefile:16: all] Error 2
> > make[3]: Leaving directory '/home/build/linux-4.19.218/debian/build/build-tools/tools/lib/lockdep'
> > make[2]: *** [debian/rules.real:795: build-liblockdep] Error 2
> > make[2]: *** Waiting for unfinished jobs....
> > 
> > I was not yet able to look further on it.
> 
> Might actually be a distro specific issue, needs some further
> investigation.

I'm really sorry about the doubled noice, so here is the stance. I can
reproduce distro indpeendent, but the initial claim was wrong. It can
be reproduced for 4.19.218:

$ LC_ALL=C.UTF-8 V=1 ARCH=x86 make -C tools liblockdep
make: Entering directory '/home/build/linux-stable/tools'
mkdir -p lib/lockdep && make  subdir=lib/lockdep  -C lib/lockdep 
make[1]: Entering directory '/home/build/linux-stable/tools/lib/lockdep'
make -f /home/build/linux-stable/tools/build/Makefile.build dir=. obj=fixdep
  gcc -Wp,-MD,./.fixdep.o.d -Wp,-MT,fixdep.o  -D"BUILD_STR(s)=#s"   -c -o fixdep.o fixdep.c
   ld -r -o fixdep-in.o  fixdep.o
gcc  -o fixdep fixdep-in.o
  gcc -Wp,-MD,./.common.o.d -Wp,-MT,common.o -g -DCONFIG_LOCKDEP -DCONFIG_STACKTRACE -DCONFIG_PROVE_LOCKING -DBITS_PER_LONG=__WORDSIZE -DLIBLOCKDEP_VERSION='"4.19.218"' -rdynamic -O0 -g -fPIC -Wall -I. -I./uinclude -I./include -I../../include -D"BUILD_STR(s)=#s" -c -o common.o common.c
  gcc -Wp,-MD,./.lockdep.o.d -Wp,-MT,lockdep.o -g -DCONFIG_LOCKDEP -DCONFIG_STACKTRACE -DCONFIG_PROVE_LOCKING -DBITS_PER_LONG=__WORDSIZE -DLIBLOCKDEP_VERSION='"4.19.218"' -rdynamic -O0 -g -fPIC -Wall -I. -I./uinclude -I./include -I../../include -D"BUILD_STR(s)=#s" -c -o lockdep.o lockdep.c
In file included from lockdep.c:28:
../../../kernel/locking/lockdep.c: In function ‘look_up_lock_class’:
../../../kernel/locking/lockdep.c:692:2: warning: implicit declaration of function ‘hlist_for_each_entry_rcu_notrace’; did you mean ‘hlist_for_each_entry_continue’? [-Wimplicit-function-declaration]
  hlist_for_each_entry_rcu_notrace(class, hash_head, hash_entry) {
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  hlist_for_each_entry_continue
../../../kernel/locking/lockdep.c:692:53: error: ‘hash_entry’ undeclared (first use in this function); did you mean ‘hash_ptr’?
  hlist_for_each_entry_rcu_notrace(class, hash_head, hash_entry) {
                                                     ^~~~~~~~~~
                                                     hash_ptr
../../../kernel/locking/lockdep.c:692:53: note: each undeclared identifier is reported only once for each function it appears in
../../../kernel/locking/lockdep.c:692:64: error: expected ‘;’ before ‘{’ token
  hlist_for_each_entry_rcu_notrace(class, hash_head, hash_entry) {
                                                                ^~
                                                                ;
../../../kernel/locking/lockdep.c:704:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
make[2]: *** [/home/build/linux-stable/tools/build/Makefile.build:97: lockdep.o] Error 1
make[1]: *** [Makefile:121: liblockdep-in.o] Error 2
make[1]: Leaving directory '/home/build/linux-stable/tools/lib/lockdep'
make: *** [Makefile:66: liblockdep] Error 2
make: Leaving directory '/home/build/linux-stable/tools'

Reverting upstream ce0b9c805dd6 ("locking/lockdep: Avoid RCU-induced
noinstr fail") on top of 4.19.218 fixes the issue.

So back to square one, and again apologies for the intermediate noise!

Regards,
Salvatore