[PATCH 1/2] ipmr: Fix RCU list debugging warning

[PATCH 1/2] ipmr: Fix RCU list debugging warning

[Amol Grover]

ipmr_for_each_table() macro uses list_for_each_entry_rcu()
for traversing outside of an RCU read side critical section
but under the protection of rtnl_mutex. Hence, add the
corresponding lockdep expression to silence the following
false-positive warning at boot:

[    4.319347] =============================
[    4.319349] WARNING: suspicious RCU usage
[    4.319351] 5.5.4-stable #17 Tainted: G            E
[    4.319352] -----------------------------
[    4.319354] net/ipv4/ipmr.c:1757 RCU-list traversed in non-reader section!!

Signed-off-by: Amol Grover <frextrite@gmail.com>
---
 net/ipv4/ipmr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 6e68def66822..99c864eb6e34 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -110,7 +110,8 @@ static void ipmr_expire_process(struct timer_list *t);
 
 #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES
 #define ipmr_for_each_table(mrt, net) \
-	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list)
+	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
+				lockdep_rtnl_is_held())
 
 static struct mr_table *ipmr_mr_table_iter(struct net *net,
 					   struct mr_table *mrt)
-- 
2.24.1

[PATCH 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro

[Amol Grover]

ipmr_for_each_table() uses list_for_each_entry_rcu() for
traversing outside of an RCU read-side critical section but
under the protection of pernet_ops_rwsem. Hence add the
corresponding lockdep expression to silence the following
false-positive warning at boot:

[    0.645292] =============================
[    0.645294] WARNING: suspicious RCU usage
[    0.645296] 5.5.4-stable #17 Not tainted
[    0.645297] -----------------------------
[    0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!

Signed-off-by: Amol Grover <frextrite@gmail.com>
---
 net/ipv4/ipmr.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 99c864eb6e34..950ffe9943da 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -109,9 +109,10 @@ static void mroute_clean_tables(struct mr_table *mrt, int flags);
 static void ipmr_expire_process(struct timer_list *t);
 
 #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES
-#define ipmr_for_each_table(mrt, net) \
-	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
-				lockdep_rtnl_is_held())
+#define ipmr_for_each_table(mrt, net)					\
+	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list,	\
+				lockdep_rtnl_is_held() ||		\
+				lockdep_is_held(&pernet_ops_rwsem))
 
 static struct mr_table *ipmr_mr_table_iter(struct net *net,
 					   struct mr_table *mrt)
-- 
2.24.1

Re: [PATCH 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro

[David Miller]

From: Amol Grover <frextrite@gmail.com>
Date: Sat, 22 Feb 2020 12:08:36 +0530

> ipmr_for_each_table() uses list_for_each_entry_rcu() for
> traversing outside of an RCU read-side critical section but
> under the protection of pernet_ops_rwsem. Hence add the
> corresponding lockdep expression to silence the following
> false-positive warning at boot:
> 
> [    0.645292] =============================
> [    0.645294] WARNING: suspicious RCU usage
> [    0.645296] 5.5.4-stable #17 Not tainted
> [    0.645297] -----------------------------
> [    0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
> 
> Signed-off-by: Amol Grover <frextrite@gmail.com>

This patch series causes build problems, please fix and resubmit the entire
series:

[davem@localhost net-next]$ make net/ipv4/ipmr.o 
  CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  DESCEND  objtool
  CC      net/ipv4/ipmr.o
In file included from ./include/linux/rculist.h:11,
                 from ./include/linux/pid.h:5,
                 from ./include/linux/sched.h:14,
                 from ./include/linux/uaccess.h:5,
                 from net/ipv4/ipmr.c:24:
net/ipv4/ipmr.c: In function ‘ipmr_get_table’:
./include/linux/rculist.h:63:25: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
  RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),  \
./include/linux/rcupdate.h:263:52: note: in definition of macro ‘RCU_LOCKDEP_WARN’
   if (debug_lockdep_rcu_enabled() && !__warned && (c)) { \
                                                    ^
./include/linux/rculist.h:381:7: note: in expansion of macro ‘__list_check_rcu’
  for (__list_check_rcu(dummy, ## cond, 0),   \
       ^~~~~~~~~~~~~~~~
net/ipv4/ipmr.c:113:2: note: in expansion of macro ‘list_for_each_entry_rcu’
  list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
  ^~~~~~~~~~~~~~~~~~~~~~~
net/ipv4/ipmr.c:138:2: note: in expansion of macro ‘ipmr_for_each_table’
  ipmr_for_each_table(mrt, net) {
  ^~~~~~~~~~~~~~~~~~~

Re: [PATCH 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro

[Amol Grover]

On Mon, Feb 24, 2020 at 01:18:01PM -0800, David Miller wrote:
> From: Amol Grover <frextrite@gmail.com>
> Date: Sat, 22 Feb 2020 12:08:36 +0530
> 
> > ipmr_for_each_table() uses list_for_each_entry_rcu() for
> > traversing outside of an RCU read-side critical section but
> > under the protection of pernet_ops_rwsem. Hence add the
> > corresponding lockdep expression to silence the following
> > false-positive warning at boot:
> > 
> > [    0.645292] =============================
> > [    0.645294] WARNING: suspicious RCU usage
> > [    0.645296] 5.5.4-stable #17 Not tainted
> > [    0.645297] -----------------------------
> > [    0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!
> > 
> > Signed-off-by: Amol Grover <frextrite@gmail.com>
> 
> This patch series causes build problems, please fix and resubmit the entire
> series:
> 
> [davem@localhost net-next]$ make net/ipv4/ipmr.o 
>   CALL    scripts/checksyscalls.sh
>   CALL    scripts/atomic/check-atomics.sh
>   DESCEND  objtool
>   CC      net/ipv4/ipmr.o
> In file included from ./include/linux/rculist.h:11,
>                  from ./include/linux/pid.h:5,
>                  from ./include/linux/sched.h:14,
>                  from ./include/linux/uaccess.h:5,
>                  from net/ipv4/ipmr.c:24:
> net/ipv4/ipmr.c: In function ‘ipmr_get_table’:
> ./include/linux/rculist.h:63:25: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
>   RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),  \
> ./include/linux/rcupdate.h:263:52: note: in definition of macro ‘RCU_LOCKDEP_WARN’
>    if (debug_lockdep_rcu_enabled() && !__warned && (c)) { \
>                                                     ^
> ./include/linux/rculist.h:381:7: note: in expansion of macro ‘__list_check_rcu’
>   for (__list_check_rcu(dummy, ## cond, 0),   \
>        ^~~~~~~~~~~~~~~~
> net/ipv4/ipmr.c:113:2: note: in expansion of macro ‘list_for_each_entry_rcu’
>   list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
>   ^~~~~~~~~~~~~~~~~~~~~~~
> net/ipv4/ipmr.c:138:2: note: in expansion of macro ‘ipmr_for_each_table’
>   ipmr_for_each_table(mrt, net) {
>   ^~~~~~~~~~~~~~~~~~~

This is a build warning due to incorrect operator precedence in
__list_check_rcu macro. This has already been reported and the patch
submitted [1]. Infact the patch is currently queued for v5.7.

[1] https://lore.kernel.org/patchwork/patch/1181886/

Thanks
Amol