linux-kernel - Re: [PATCH 2/2] ipmr: Add lockdep expression to ipmr_for_each

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Date:   Mon, 24 Feb 2020 13:18:01 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     frextrite@...il.com
Cc:     kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org, kuba@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        joel@...lfernandes.org, madhuparnabhowmik10@...il.com,
        paulmck@...nel.org
Subject: Re: [PATCH 2/2] ipmr: Add lockdep expression to
 ipmr_for_each_table macro

From: Amol Grover <frextrite@...il.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@...il.com>

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

[davem@...alhost 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) {
  ^~~~~~~~~~~~~~~~~~~