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Date: Sun, 26 Jul 2020 08:49:03 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: kernel test robot <lkp@...el.com>
Cc: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>,
kbuild-all@...ts.01.org, linux-kernel@...r.kernel.org
Subject: Re: [rcu:dev.2020.07.14a 64/73] include/linux/rculist.h:727:30:
error: left-hand operand of comma expression has no effect
On Sun, Jul 26, 2020 at 11:28:55AM +0800, kernel test robot wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2020.07.14a
> head: aace6daf32cce6b644083754c7be6260aae439db
> commit: 93d62a873f87bf69209a5c29d62b9497888de6d6 [64/73] kvm: mmu: page_track: Fix RCU list API usage
> config: i386-randconfig-a006-20200726 (attached as .config)
> compiler: gcc-9 (Debian 9.3.0-14) 9.3.0
> reproduce (this is a W=1 build):
> git checkout 93d62a873f87bf69209a5c29d62b9497888de6d6
> # save the attached .config to linux build tree
> make W=1 ARCH=i386
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
Good catch, but this commit has been superseded by 74e71f01ff46 ("kvm:
mmu: page_track: Fix RCU list API usage"). As always, thank you for
your testing efforts.
Thanx, Paul
> Note: the rcu/dev.2020.07.14a HEAD aace6daf32cce6b644083754c7be6260aae439db builds fine.
> It only hurts bisectibility.
>
> All errors (new ones prefixed by >>):
>
> In file included from include/linux/pid.h:5,
> from include/linux/sched.h:14,
> from include/linux/kvm_host.h:12,
> from arch/x86/kvm/mmu/page_track.c:14:
> arch/x86/kvm/mmu/page_track.c: In function 'kvm_page_track_write':
> >> include/linux/rculist.h:727:30: error: left-hand operand of comma expression has no effect [-Werror=unused-value]
> 727 | for (__list_check_srcu(cond), \
> | ^
> arch/x86/kvm/mmu/page_track.c:232:2: note: in expansion of macro 'hlist_for_each_entry_srcu'
> 232 | hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
> | ^~~~~~~~~~~~~~~~~~~~~~~~~
> arch/x86/kvm/mmu/page_track.c: In function 'kvm_page_track_flush_slot':
> >> include/linux/rculist.h:727:30: error: left-hand operand of comma expression has no effect [-Werror=unused-value]
> 727 | for (__list_check_srcu(cond), \
> | ^
> arch/x86/kvm/mmu/page_track.c:258:2: note: in expansion of macro 'hlist_for_each_entry_srcu'
> 258 | hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
> | ^~~~~~~~~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
>
> vim +727 include/linux/rculist.h
>
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 688
> 1cc523271ef0b63 stephen hemminger 2010-02-22 689 #define __hlist_for_each_rcu(pos, head) \
> 67bdbffd696f29a Arnd Bergmann 2010-02-25 690 for (pos = rcu_dereference(hlist_first_rcu(head)); \
> 75d65a425c0163d Linus Torvalds 2011-05-19 691 pos; \
> 67bdbffd696f29a Arnd Bergmann 2010-02-25 692 pos = rcu_dereference(hlist_next_rcu(pos)))
> 1cc523271ef0b63 stephen hemminger 2010-02-22 693
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 694 /**
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 695 * hlist_for_each_entry_rcu - iterate over rcu list of given type
> b67bfe0d42cac56 Sasha Levin 2013-02-27 696 * @pos: the type * to use as a loop cursor.
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 697 * @head: the head for your list.
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 698 * @member: the name of the hlist_node within the struct.
> ddc465936643108 Jonathan Neuschäfer 2020-03-05 699 * @cond: optional lockdep expression if called from non-RCU protection.
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 700 *
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 701 * This list-traversal primitive may safely run concurrently with
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 702 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 703 * as long as the traversal is guarded by rcu_read_lock().
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 704 */
> 28875945ba98d1b Joel Fernandes (Google 2019-07-16 705) #define hlist_for_each_entry_rcu(pos, head, member, cond...) \
> 28875945ba98d1b Joel Fernandes (Google 2019-07-16 706) for (__list_check_rcu(dummy, ## cond, 0), \
> 28875945ba98d1b Joel Fernandes (Google 2019-07-16 707) pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
> b67bfe0d42cac56 Sasha Levin 2013-02-27 708 typeof(*(pos)), member); \
> b67bfe0d42cac56 Sasha Levin 2013-02-27 709 pos; \
> b67bfe0d42cac56 Sasha Levin 2013-02-27 710 pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 711 &(pos)->member)), typeof(*(pos)), member))
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 712
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 713 /**
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 714 * hlist_for_each_entry_srcu - iterate over rcu list of given type
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 715 * @pos: the type * to use as a loop cursor.
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 716 * @head: the head for your list.
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 717 * @member: the name of the hlist_node within the struct.
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 718 * @cond: lockdep expression for the lock required to traverse the list.
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 719 *
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 720 * This list-traversal primitive may safely run concurrently with
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 721 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 722 * as long as the traversal is guarded by srcu_read_lock().
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 723 * The lockdep expression srcu_read_lock_held() can be passed as the
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 724 * cond argument from read side.
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 725 */
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 726 #define hlist_for_each_entry_srcu(pos, head, member, cond) \
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 @727 for (__list_check_srcu(cond), \
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 728 pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 729 typeof(*(pos)), member); \
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 730 pos; \
> bd4444c47de914a Madhuparna Bhowmik 2020-07-12 731 pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
> b67bfe0d42cac56 Sasha Levin 2013-02-27 732 &(pos)->member)), typeof(*(pos)), member))
> 82524746c27fa41 Franck Bui-Huu 2008-05-12 733
>
> :::::: The code at line 727 was first introduced by commit
> :::::: bd4444c47de914a27b650f029d46efbbb6809765 rculist : Introduce list/hlist_for_each_entry_srcu() macros
>
> :::::: TO: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> :::::: CC: Paul E. McKenney <paulmck@...nel.org>
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
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